What makes the material slip over to the side
when you are topstitching things not just straps
but I've had it happen to other parts as well?
Is it because seams arn't sewn straight? thanks Rita

If it's slipping off the edge, it's usually because the feed dogs are feeding on the side of the fabric, but the other side they're "flapping in the breeze."
If you can move the needle position on your machine, try moving it as far to the right as possible so the fabric covers both the left and right feed dogs.

Maybe try using a walking foot? :D:D:D

Yes, that would help.

Ok thanks will try both------------Rita