HSA Prorated Contribution & Excessive Contribution in 2019

Hi, I'm in the process of preparing my tax return and was told that I had an excessive contribution of $2073 in 2019. I'm skeptical about this amount and I wanted to double check if that is really right. 

Here are my facts: 

  • Under 55
  • Started working full time in mid May 2019. No job Jan-April 2019 as a student. 
  • Had insurance from a company Jan-April 2019. On company medicare plan starting May.
  • Had no HSA before 2019 till this current job 
  • Contributed a total of $3240, $2940 of which is from my paychecks) to my individual HSA account in 2019

The maximum HSA contribution in 2019 is $3500.

Assuming that 

  • My HSA eligibility started in May (the month I started working), then my max HSA contribution is 3500/12 x 8 = $2333 then excessive contribution is $3240 - $2333 = $907
  • OR My HSA eligibility started in Jun, then my max HSA contribution is 3500/12 x 7 = $2042 then excessive contribution is $3240 - $2042= $1198

Both scenarios suggest different excessive contribution different from what is suggested above. Can an expert please help me out? Thank you!