It really depends on the lender. My advice to you is to stop looking at rates if you have already locked in. The agreement that you signed said that if rates go up the lender loses, but if rates go down you lose. In the end you need to honor your agreement unless the bank is willing to let you relock.
Do yourself a favor though and stop watching rates. I know that this really hard to do, but you must do it or you will drive yourself crazy.
We have a client under contract that his lender shopped around and found a different investor and got our Buyer a better rate. You may have to do this to close on time.
If you already closed you may want to look into doing a re-fi