First of all, UCR is a very good university. You can do well starting with with a bachelor’s degree from UCR.
When you apply to graduate programs, you will need to provide them with transcripts that list every grade that you got in college or university. However, what you did in high school will not matter (unless you took courses at a college while you were in high school).
You can forget about any regrets you had about how you did in high school. Instead focus on doing very well in university.
When applying to graduate programs, your grades in university will matter. Your letters of reference will matter, but will typically come from professors that you will get to know after you get to university. Your research experience will matter, but this is typically something that you will get after you get to university. Internships will matter, but again this is something that you can get after you get to university.
Generally speaking getting accepted to a master’s degree program after completing a bachelor’s degree is not likely to be any more difficult compared to getting accepted to a university from high school. Getting accepted to a PhD program can be very challenging and competitive.
I have a daughter who is currently studying for a PhD. She is just completing her first year, so we still remember pretty much what she did to get accepted to a good PhD program. One thing that she had was very good grades in university. You can help yourself here by attending every class, always paying attention, keeping way ahead in your homework, and looking for help early if you need any help. She also got involved in research while in university. She specifically got very involved in lab work. I think that her first research experience was over the summer after her second year of university, but it is possible that she might have started earlier than this. The first research project that she was involved in was not quite what she wanted to do, but she took it very seriously and did well in it. After this the second research project that she got involved in was what she wanted to do. This research experience was quite helpful after she graduated and got a research job. Then she worked for a couple of years in a research job before applying to graduate programs.
For applying to master’s degree programs that might be all that you need to do.
However, she was applying to PhD programs, which are more competitive. One thing that she did was to look at the research in her field that was being done at every university that she was thinking of applying to. She read the papers in her field that had been written by each professor at each university that she was applying to. In filling out applications for PhD positions, she was able to explain how what she wanted to do was related to the work that was already been done at each university. Then before interviewing with any specific professor, she re-read the papers that the professor had written. She went into each interview with at least one question that she was ready to ask the professor about the professor’s research. This attention to detail can be helpful when applying to PhD positions. This is however way, way in the future for you and is something that you do not need to think about right now.
The first recommendation is for you to attend every class, sit near the front if you can, and always pay attention. Stay way ahead in your homework. Starting your homework early has multiple advantages. One advantage is that this is likely to help you to pick up just a little bit more in your next class. Even if the only thing that you learn from trying to do a particular homework problem is “I do not fully understand this concept”, this might still help you to pick up a bit more in the next class. Sometimes a homework problem will take longer than you expect, and if you start early you might have time to finish. Also, there are likely to be some times when you need to seek out extra help, and starting your homework early will give you time to do this. The last thing that I noticed once I finally got the point of staying way ahead in homework: Often actually doing the homework is easier and less stressful compared to worrying about the homework that you are not getting done. The number one thing that I would have done differently would have been to pick up the habit earlier of always staying way ahead in homework.
It can be helpful to get to know your professors. However, it is important to be a reasonable and responsible person. You do not want to be stalking your professors. Be reasonable and attentive and willing to ask questions, but also be ready to listen.
It sounds like you are starting off at a very good university in September. It also sounds like you are starting with a determination to work hard and do well. Congratulations! You can do this. Best wishes.