Missed Qualifying Event

So say I got married in May and forgot to tell my insurance, and am now looking at an MRI and surgery, how screwed am I?

I begged my husband for months to get the info from his employer about putting me on his plan since we got married and that’s a qualifying event. He waited too long and we missed the window. I currently have ACA insurance through the marketplace (OH), I get a $300 credit on my plan each month so my payment is only $40. I just recently had an injury and am looking at some hefty medical expenses. When talking to the admins at my doctors office this past week, I realized I never informed my insurance of the life event.

My question is: do I finish out the year and hope they don’t find out I got married then switch to his employers plan during open enrollment? Do I tell my insurance asap that I got married but can’t get on my husbands insurance and hope they’ll let me keep my plan? I worry about tax time, if we say we got married on our taxes, I’m worried I’ll have to pay back 7 months worth of the monthly $300 tax credit I’m receiving on my insurance plan.