Can you lock in your interest rate?

Yes. A rate lock holds your quoted rate for a set period while your loan is processed, subject to your lender's terms. Locks can have a fee, an expiration, and rules for extension, so ask your lender when to lock and what happens if closing is delayed. Generally you want to lock closer to closing than not, but that's a conversation between you and your lender about current economic trends. Rates change often, and no one can predict where they will go.