Credit dropped, what happens to mortgage?

I was pre-approved for a mortgage, with a score of 650, about a month ago. I found a house, and the offer was accepted. I have a card with a limit of $300, that I got a while ago simply to build credit. Recently, I let the balance go up to 287 then made a $50 payment. My credit report from May 6 now says that it has dropped to 520, all due to that credit card balance. What's going to happen now? I'm so worried I can barely eat or sleep. Thanks for any insightful answers.

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