Biology Major at UDub

I love UDub. It is beautiful and the students are passionate, the city around it magnificent and accessible. While I’d love to go there, I am interested in majoring in biology with an environmental impact focus (hopefully med or dental school after, possibly non-profit work).
I am a little hesitant about the size of classes at UDub, particularly in the sciences, as well as the rigor. Science (particularly chemistry) isn’t my strongest suit, but I believe I can succeed when allowed ample opportunity to talk to people about material. Given this, do any UW students have any say or advice on science programs at the university, their size and accessibility of professors, and whether a major in biology would best be pursued at a big state school with research and intern opportunities that could help to advance my application or at a smaller school (say Lewis & Clark, or comparably, Montana State, which I could attend for biology but at a very low cost)?
Also, is the biology track more difficult to be accepted on as an undergrad (it is considered an “open” major)? I am a pretty strong student (35 ACT, 4.54 W/ 3.74 UW GPA and mostly Honors, all AP’s this and most of last year, some good EC’s), but received B’s in Physics and Chemistry and 3/4 math classes (all of which were honors or AP’s) and am a little distraught by this.
Any input would be much appreciated. Thanks!