It has been a terrific week for rates - so, assuming you are a strong candidate, it is possible that that rate is real and trustworthy. When you get your paperwork (it HAD to be sent out within 3 days of your application, by law, so watch for it in the next few days), look it over carefully to make sure that costs and fees are in line with what was represented to you. If it is NOT what you expected, call someone else quickly while rates are still low!
Once you are satisfied, make sure you do everything in your power to turn your loan around quickly - provide documentation requested, etc. If you stay within your lock timeframe, you should keep that excellent rate - and pat yourself on the back for timing!!