When you say "When I answer question about contributions made in 2019 for 2018 on Form 5498-SA", I don't know what you mean, because there is no such question - that is, there is no such question as asks for the amount of contributions from the 5498-SA.
There IS a question that asks if your employer told you about any contributions not for the current year, and when you say "yes", it exposes three more lines, one of which is enter any amount of contributions that your employer made in 2019 for 2018. Is this the line you are referring to?
This $200 - did you make a direct contribution to your HSA in 2019 for 2018? If so, the line above is the wrong place to enter it. You enter this $200 instead as a "personal" contribution on the "Let's enter [name]'s HSA contributions" (see screenshot below) on the second line.
If, however, the $200 was indeed made by your employer in 2019 for 2018, then enter it on the "any amount of contributions that your employer made in 2019 for 2018."
You need to look into the transaction log for your HSA. The HSA is yours, not your employer's, and the activity log for your HSA is probably available online at your HSA custodian's website.
Compare what you see in the activity log to your W-2 - does the total of your deposits in 2018 add up to $2050 like on the W-2 or to $1,850 like in box 2 of the 5498-SA? IS it possible that the $200 was an employer deposit in 2019 for 2018 but the employer listed it in the code W amount on the W-2? It does happen that an employer adds contributions in one year for their purposes, but the HSA adds the amount to a different year (say, if the employer makes the deposit on December 30, but the HSA doesn't report it until January 2nd).
In any case, the most likely outcome is that the employer reported it in the code W amount but the HSA thinks it's a 2019contributions for 2018. If you discover that the $200 2019 contribution for 2018 was included in the code W amount, then don't add the extra $200 anywhere - because it's already in the code W amount.