I have been in contact with a positive covid case. we were is a classroom for five hours. we were both wearing masks. she tested + on sat. 12/3. i decided to go for a test today. no symptoms. would i still need to isolate if the result is negative?

COVID 19 test: If your contact with her was on or before 3 DEC 2020 - that means you will be 12 or more days out from your exposure. The mean incubation period is 5 days. About 97% of the people who get infected & develop symptoms will do so within 11 to 12 days. Thus a negative test at this point should be accurate. You would not need to quarantine further at that point.