Buy a cheap pair of calipers - I think plastic digital ones are in the US$40 range. They're pretty useful when you want to do a quick "paranoia check" on anything physical.
I think I've made layout mistakes on imperial/metric conversions, radius/diameter, drill size/plated size, left/right/up/down swaps, and having mounting holes offset by 100 mils due to PBKAC issues... Thankfully, I don't think I've made the same mistake twice, I just wander into new ones every now and then.
Also, be sure to have enough slack in the hole measurements so that you don't have to press-fit anything. If you want to be able to desolder the stuff, you want the hole to be as loose as reasonably possible...