I do not see Stanford happening, for undergraduate study. Whether UCs are possible might depend upon which UC, and how your sophomore year went as compared to freshman year (my understanding is that UCs on the most part do not care about freshman year).
However, your uptrend, assuming that you can keep this up, is likely to help you a lot. Lots of good universities may be possible.
If you ever get to the point of applying to graduate programs, high school will not matter. DE classes that you took at a college might be considered, but high school classes will not matter. Also, if you look at the graduate students at top universities (including Stanford, where I got my master’s degree), they come from a huge range of undergraduate schools. Graduate study however if it happens at all is a long way in the future.
Perhaps more important, you can get an excellent undergraduate education at any one of a huge range of universities.
This is correct. Do your best from now on.
I am a bit concerned that you might have overloaded yourself with this year’s courses. Work Hard. Keep ahead as much as you can. Get some sleep. Do the best that you can, and see how it comes out.