Mortgage question...need help!?

We received the Uniform Residential Loan Application from our broker and the interest rate is higher than we want. He says we are not locked in and won't be until it comes down (if it comes down). Yet, we are supposed to sign this application and the mortgage disclosure documents that have the high rate on it. By signing it, are we going to be agreeing to this rate? (I'm a first time homebuyer and pretty confused when it comes to the mortgage stuff.)