I think the general recommendation is to have letters of recommendation from 1 humanities, 1 STEM, and 1 other (for institutions that require 3). Some universities may let you submit additional ones as well, but it is not required and if submitting more than the required, I would make sure the extra one would an exceptional LOR that describes you in a way that the other LORs can’t.
I’m not familiar with the Common App’s setup, but I would certainly find a way to include some of your science-related ECs.
But taking your classical music ECs as an example, I could see how it could go from 7 different items to the 3 asterisked items (assuming that City Youth and County Youth Orchestras are the same)
- Private Violin Lessons: (First thing I would cut from this section…with all your orchestral experience, this will probably be assumed.)
- School Chamber Orchestra: Concertmaster Gr. 9-12 (Would eliminate if there is not sufficient room for other ECs)
- *All-County Orchestra: First Vioinist 2020, Concertmaster 2022 & 2023?
- City Youth Orchestra: First Violin Gr. 9-10
- *County Youth Orchestra: Asst. Concertmaster 2022, Concertmaster 2023 (Are the city and county youth orchestras different, or was it renamed between sophomore and junior years? If they are the same, combine all into one.)
- *Mentoring Musical Minds: Explain the impact of what has been going on (How many kids tutored? How many 30-minute lessons provided? How long has this been going on? How many volunteers? Is there a plan for this organization continuing once you graduate high school?)