If demand is strong enough that the clearing price would exceed the $9.90 cap, the sale is oversubscribed. Here's what happens:
Every successful bidder pays the cap price ($9.90)
Tokens are allocated first-come, first-served, in the order bids were placed, until the 2,000,000 tokens are exhausted
Bidders whose orders can't be filled receive a full refund of their uncommitted USDC
What this means for you
If you're confident you want to participate, bid early. In the oversubscribed scenario, the time you placed your bid determines whether you receive an allocation. A bid placed on September 1 outranks an identical bid placed on September 3.
Bidding early carries no price risk. You always pay the clearing price, never your bid price, and if the auction clears below your maximum you simply get more tokens for your commitment.