Do you mean your offer has been ACCEPTED? ("excepted" means something totally different). If the house does not appraise for the agreed upon purchase price, then several things can happen:
1. Seller reduces the purchase price; or
2. Buyer comes up with the difference; or
3. Combination of #1 and #2; or
4. If buyer and seller cannot come to a resolution you can terminate and find another house.
FYI -- you really should be asking your REALTOR this question.