Deep breath. You are not overreacting. You just have a pile up of frustrating learning situations. And guess what? You aren’t acting like a child, you are trying to solve the problems and it isn’t going smoothly. Welcome to adulthood. Some days or weeks are just plain hard. Problem solving is an ongoing process.
You are struggling with some learning tasks that sound difficult. You are doing the right thing by being honest that it scares you or you aren’t getting it with the professors and asking for help. Rather than compare yourself to others and feel stupid, find someone who is getting it and ask them if they would spend some time with you to show you. If you can take your time without so much in class pressure you might feel more comfortable practicing. You can’t expect to know how to do these very different new things in one or two tries, it will take practice.
As far as preventing forgetting things, having a checklist that you look at every time you make a transition,might help. Staying as organized and keeping routines can help.
Keep trying hard, keep problem solving, you can do this even if it is hard.