Originally Posted by FBinNY

No Q-factor wouldn't come into play.

As you describe the situation, I assume the chain is coming off to the outside, which may be because the crank is too far inboard. You can measure chainline by measuring from the tips of the teeth on the outer ring to the down tube, add 1/2 the D/T diameter, This should be about 46mm (plus or minus 2mm is OK). If yours is more inboard than that, and you have a spacer on the left side of the spindle that you can move to the right do so.

I prefer to set all my bikes up with the chainline outboard of that 46mm figure because it improves the chain line for the gears I ride most (outer ring with outer half of the cassette), so feel free to go to the high side of the 46mm distance.

If you cannot improve the chain line there are a few more tricks available, but they involve the use of a file, and many balk at modifying hardware. Though it's fine if you know what you're doing.