Withdrawing an acceptance to a USMD school for hopes for a "better" acceptance in the future would be demonstrably poor decision-making and personal malpractice on how to live one's life.
Unless the school has some sort of major violations or something along the lines of losing their primary teaching-hospital affiliate, then take the golden ticket and run (assuming you get in). School prestige helps, but there are multiple other factors are that are of significantly greater importance for matching into competitive fields.
Think of school prestige as the rider on an elephant, and you are the elephant. That rider might help pull left or right, but the elephant is going to go wherever it wants to go.