1. Nevermind the ruffians

2. Make sure you VERY tightly torqued the lugs on the breaker AND the outlet.
3. Test the connections across X and Y (both legs) for 240-250VAC
4. Feel free to test the legs independently to Neutral, although the UMC doesn't use it.
5. Test the Neutral to Ground for ohms, as they should be close to 0 if they've met at the breaker box.
As for the UMC, as soon as you plug it in, it should cycle through then give you one green light if it's getting proper circuit. Only pulling a proper load (like a car) will tell if the amps will hold through it. Check the UMC's plug adapter temperature as well as the breaker for any problems. The UMC's cord should be the warmest of the whole thing when drawing 40A.
Good luck, and congrats on the DIY! I've done 3 of them with ZERO issues. TORQUED LUGS is the key to a successful install.