I finished bachelors in spring 2020 as a part-time student and started masters in fall 2020 as full time student. How do i answer earning 4 yr college credit before 2020?

You need to answer yes to that question, since you finished your bachelors in 2020.  

I believe the question is: "Did you complete 4 yr college credit before January 1,  2020?" The answer is NO.

This means the undergrad expenses  (but not the grad expenses) are eligible for the more generous American Opportunity Credit (AOTC), assuming you (and/or your parents did not already claim it 4 times in the past).

The alternate is to combine your undergrad and grad expenses and claim the Lifetime Learning Credit (LLC).  You may only claim one credit.  That is, you may not claim the AOTC for the undergrad expenses AND the LLC for the grad costs.