I think it looks great for a boy! Well done for losing your sewing machine cherry
What I do with my loose ends -
generally you will end up with one thread on the top and one on the bottom of your fabric wherever you start or stop sewing - sometimes they both end up on the back in which case you can skip the next step.
Gently pull on the thread on the back until it draws through the thread on the front - you may need to use a pin to help grab the little loop that forms as you pull it through
Tie these two together into a double knot right at the fabric surface
Thread the two ends onto a hand sewing needle
Stitch into just the back layer of your fabric right by the knot and do one stitch as long as you can then pull the needle all the way back out and trim the threads at the fabric
I hope this makes sense, it works well and looks neat