It is cheating to use your tongue to U-block and get the single hole!
You need your tongue for other techniques down the road, such as bending (very important) and actual tongue blocking, as Ian mentioned. So.. yep, loose the U-block and just use your lips.
It’s also natural for your face to be a little sore when starting out, as yep, those muscles need to be activated. That’s one reason a little everyday (like 15 minutes) is better than one huge session once a week. You need to build up the muscle memory!
Welcome, and all the best!