Leather will stretch if you get it wet. I'll be easy to pull it that little bit wider. Problem is going to come when you wear it. The strain pulling the leather lengthwise instead of width wise will pull it back to where it was before.
You gotta remember, that's a dead animal hide. They can cut it perfect, but half a millimeter isn't hard to lose when they finish the edges.
You could try getting some edge paint and just hitting right around the lug hole. That actually might be your best bet. You can peel it off if you need. Or get something called UW 13/8 it's a edge gloss. It's basically like a clear liquid plastic. Use a q-tip and just hit that end of the strap that sits between the lugs.