You can increase your bid at any time while the auction is open. Both your maximum price and your USDC commitment can go up.
You cannot:
Lower your maximum price
Reduce your commitment
Withdraw or cancel a bid
This is by design: bids that can only rise create honest price discovery. Treat your bid as a real commitment, because it is one.
If your bid ends up below the final clearing price, it simply doesn't clear. You receive no tokens and your full USDC is returned. So the practical worst case for an outbid participant is a refund, not a loss.