I just drilled my motor mount for my Sig Lt-40 ARF. I'm putting a TT .46 Pro on it. After I was finished drilling the holes I noticed that the holes I drilled were not centered on each motor mount arm, the holes on the left side were further to the inside than the right side. The holes on the left side are approximately 3/16" in from the edge of the left arm. Will this be strong enough to keep the motor secure, or should I buy a new mount and re-drill the holes? The motor appears to be in the proper position, but I just want to know if I messed up.

I think you be okay with it, but keep an eye on it after running the engine up, and check it regularly once you start flying it.
Dennis-

Agree with DBC -- It should hold up OK in normal use -- it could fail more easily in a crash -- but you won't do that

3/16" edge distance should probably hold any .46 engine made.

You'll be fine. It's a little difficult to get those holes "dead on". Make your first couple flights short and check out the mount.

DaveB