Have you decided what you want to do with a degree in biology or chemistry?
Are you thinking of possibly being premed and considering medical school? If medical school is a possibility, then you should budget for a full 8 years of university. If you ignore budget and attend private universities, then you could end up spending something like $900,000 over those 8 years. You might want to make sure that your parents are okay with this. Even doctors do not make enough money for it to be easy to pay off medical school loans.
If you are more interested in research, then some graduate degree is still a possibility. PhD’s are usually fully funded (with a stipend that is barely enough to live on, some “parent enhancement” of the stipend might help but it would likely be relatively easy for high income parents). Master’s degrees are usually not funded. You might want to figure on something north of $100,000 per year for two years for a master’s degree.
Otherwise I agree that your guidance counselor at a “Prep feeder school” should be quite good and should be able to estimate your chances at highly ranked universities.
To me you look competitive for highly ranked schools (Ivy League and other similarly ranked schools). However, so are most of the other applicants. You should look at these as reaches, even if you are a legacy student. Make sure that you also apply to safeties.
And of course you should be focusing on finding schools that are a good fit for you. You are likely to have many schools that would be happy to admit you (particularly at full pay), and should find one that you like.
You might want to visit some smaller schools (Bowdoin, Colby, Dartmouth College) and some larger schools (perhaps Harvard, Tufts, BU, Northeastern, …). You should also look at some schools for which admissions is safer, such as U.Maine or UVM or UNH or U.Mass. You also might want to think about how far away from home you would want to be (is Stanford something that you want to consider? It would of course be a reach, but does have good tennis facilities and a team). I do not think that I would fly across the country to attend a university that is just as good as U.Maine and only 2 or 3 times the price, but you might want to think about whether you want to fly across the country for a highly ranked school. Remember that if you are flying home for Christmas, even if you are somewhere like Stanford where you will not get snow at that end, you are still very likely to hit snow at your home end. We have had a child stuck due to a cancelled flight home or a cancelled flight back to school.
It is not necessary to attend a “top 20” university for your bachelor’s degree to do well in life, nor to get accepted to “top 20” graduate programs. We do have some experience with someone attending somewhat lower ranked universities for a bachelor’s and then attending a highly ranked graduate program. What you do as an undergraduate student is going to be more important than where you do it. I do think that you are competitive for “top 20” universities. This does not necessarily say whether or not you will get accepted to any of them, nor whether they would be a good fit for you.
The last wild thought that comes to mind is that since you are in Maine, Canada is not all that far away. We do have some experience with both the English language universities in Quebec (McGill, Concordia, Bishop’s) and a few of the universities in Eastern Canada. Let us know if you would like any information on them.