When you're promised a "rate lock" from your lender, it means that you are guaranteed to get a certain interest rate for a determined period while you work on your application process. This keeps you from going through your entire application process and discovering at the end that your interest rate has gotten higher.
While there are several lengths of rate lock periods (from 15 to 60 days), the longer ones are usually more expensive. You can get a longer period for your lock, but in doing so, will probably have a higher interest rate than you would with a shorter span of time
In addition to choosing a shorter rate lock period, there are more ways you are able to get the best rate. A larger down payment will give you a reduced interest rate, since you will have more equity at the start. You can pay points to lower your interest rate over the loan term, meaning you pay more up front. One strategy that makes financial sense for many people is to pay points to bring the rate down over the life of the loan. You'll pay more up front, but you'll save money in the end.
Do you have a question regarding a mortgage program?