First, are you SURE you originally deducted it on Schedule C? If it was your own insurance, it should NOT have been on Schedule C. It would have ended up as the Self-Employed Health Insurance Deduction on Schedule 1. In TurboTax, that is done automatically when you enter the 1095-A and then say it was part of your business.
Assuming you filed the original correctly and claimed the deduction on Schedule 1, then the 'added back' amount should be on Schedule 1, not Schedule C.
But that may still result in the same problem. While there are several possibly reasons why you are encountering that result, I suspect it is this: The original IRS guidance gives three options to calculate things. The first and most optimal one sometimes doesn't work out right, so they give an "alternative" calculation. Sometimes that "alternative" calculation gives really weird results like what you are seeing. The third option is "another method that produces amounts that satisfy applicable tax law". TurboTax does not do anything for that option, but that is the option that likely would work best for you. It could require some gruesome manual calculations though.
If that is what is causing it, a possible work-around is to contribute to an employer retirement account, such as a SEP. While you could contribute more, hypothetically contributing $242 to your SEP would exactly offset the added $242 (assuming you correctly add it to Schedule 1, rather than Schedule C).
