I advise what I always advise. Submit accurate documents, always. Submit consistent information, always. Correct any inaccuracies before you file, always.
Very simple set of parameters and (also) aligned with the terms of service on this site.
The exemption and tax tables for single and MFS are the same, exemption $12,950 and exactly the same tax rate tables. OP faces no penalty on a corrected return regardless of what it is corrected to say.
OP has three choices outlined in the IRS vast and convoluted rulebook. MFJ with ITIN, MFS, or HOH with a qualifying dependent. My advice is to correct that error before moving forward and my advice is aligned with the rules and requirements of the agency. No combination of words and sentences from anyone is going to change point #1 and it is up to the OP to choose what to do moving forward.
What I DO know is this. Taxes are used as “proof of validity of marriage” in many steps of the immigration process. I steer applicants towards getting it right from day one, the beginning of the marriage.
You may advise otherwise if you wish and if you do so I will assuredly not pick a public argument with you about it. So kindly settle down and get back to advising the OP, not arguing with passport holding members who are done with USCIS and have completed this process.
This discussion is over from my side.