IF this is your only Sig, let me just say there is a learning curve to the trigger. I have gone throught the same thing with mine. Had to put it on a sand bag to prove to myself that it was me and not the gun. Things got better after that. Seems that some people have problems with Sigs and others can do great with them from the get-go. I know that if you are (were) a Glock person, the grip angle itself will throw you off. Just practice, practice, and practice with the trigger to make sure you are not jerking it. It will pay off. I know for a fact that my Sigs are more accurate than I can be at this time. Good luck.
Oh, I do not have any issue with my P220 SAO however, just goes to show that the trigger on a Sig does have a learing curve.