Send it to Smith, they'll fix it. Request a pre-paid box to mail it in as well. And a spare mag or two for your trouble.
I got a Sigma as my first handgun when I was 15 or so because it was cheap and I was able to swing it as a Christmas present. The trigger sucks but it has been 100% reliable.
HOLD THE PHONE....
If you thought it was an M&P, paid $400 for it, THEN ask if it is a good gun I would suggest that you make sure it is not a molding mark in the frame. I have a feeling it is based on other posts. I'm sorry man, but they let you carry a gun?