HSA/HDHCP vs Medicare

I am in a private insurance plan, employer-provided. It is a HDHCP (or whatever that is this year). I contribute the maximum to my HSA including employer contributions. I am Medicare eligible - I presume if I enroll in Part A I would lose the deductibility of the HSA contributions, true? The bad news is i enrolled anyway, but yesterday, un-enrolled. Am I still screwed?