This post would be better if placed in "First Year Help". However, regarding your question, did you not receive the offer of admission letter which states the amount of % you can safely drop? Conditional offer.
If it's high school summer school, I think I read somewhere that Mac doesn't take that into account this late. I could be wrong though...
I would say go ahead, since it's not the payment as of yet, just an agreement. If you end up not going, they probably won't charge you.
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