Do I use box 2 on my 5498 SA as my contribution amount? or use my 1099 SA?

[NCperson]

if you contributed through your employer only, it's already on the W-2.  nothing more to do.  There should be a code 'w' in box 12 of the W-2 which shows what you contributed. 

[dmertz]

To use Forms 5498-SA to determine the amount you contributed for 2019, start with the amount in box 2 of your 2019 Form 1099-R, add the amount in box 3 of your 2019 Form 5498 and subtract the amount in box 3 of your 2018 Form 5498.