Science fair?

Hi! I’m currently a junior and I’m interested in studying chemistry/biochemistry in college. I’m in 3 AP courses, and I feel like my math/science grades are not as high as they should be. (I got a B- in first semester honors precalc…) Also, I don’t have very many science extracurriculars. Finally…science research is something i’ve always wanted to try doing! That’s why I’m thinking about doing a project this summer to submit to ISEF, STS, or a similar science fair (if I don’t get into a summer program). I just wanted to hear from people who have done science fair projects, or know others who have:

What should my “timeline” look like? When should I start my project, and around when should I be mostly done? Can I use an AP Research project for something like this (data collection starts in January), or should I start later?

Also, if you have any other recommendations for ways I can get involved in STEM as a second-semester junior (both because I enjoy it and to strengthen my apps) I’d appreciate it! Thank you!(:

Also…do you think my B- will hurt me a lot in admissions? How can I make up for it?

thank you <3