Honestly. I'd call them and tell them what happened. If you want the proof I'm sure you will have to send one back...but since you got two you can pick the nicer one and return the other.
Part of me wants to take them to task for this, but who's gonna listen? If I express my displeasure to customer service, my complaint will be canned, and nothing will be done. I'm out what? $2 for the difference between an proof and an uncirc? I'll just order up another proof, and God help 'em if they get it wrong this time........
They should allow you to keep the second uncirculated and send you the proof for free. Oh wait, this is the US Mint we are talking about here.