Your payment is based on the following variables, loan amount, time and rate. If all of these remain the same, so will your payment. If the rate you lock in is different, or you choose a different loan program your payment will change.
The other areas your payment may change will be if your lender sets up an escrow account for property taxes and or insurance. Approximately 1/12th of your annual cost of either of both of these costs could be added to your monthly payment.