I'm lucky to have a space (with nothing killable behind it) in which to practice, this was at 15m but I can go up to 30m (if I don't care about having any grouping ... I'm still quite new)
What a lovely space to practice, I'm quite jealous!
Keep an eye on that bow hand grip. You want to make sure you keep a loose, open grip with the pad of your thumb pressing forward against the bow. That should be where most pressure goes.
Hand/knuckles should be at about 45° and fingers barely touching. It might help to use a finger sling to keep yourself from gripping. This helps to close up groups a lot!
Take a look at this illustration for more guidance.
I always wiggle my fingers when pre-tentioning, but close them before aiming otherwise I drop my bow on release, lol ... similarly, if my hand is at a 45 degree angle then the bow sits on my thumb which would be very painful to draw against. Weird hands, I guess!
If it is sitting on your thumb you have rotated your hand too far around towards the front/side of the bow.
Try staying behind the bow and putting pressure on the big thumb muscle of your palm. Use that to push straight forward and your hand should rest very comfortably.
Do a search, see if there's a club near to you - it's the best way to get started! (my nearest club is an hour away, otherwise I'd use their facilities which are a lot lot nicer, lol)
Archery is awesome, everyone should at least try it :-)