I can relate. I inherited 3 raised boxes this year, put them together, and they're still waiting to be set out and filled. Maybe next year me will finish what this year me started.

I will say, setting up a small basic herb garden and lettuce is super easy, low maintenance, and forgiving as far as growing plants goes.

You gotta pick the leaves regularly, that doesn't look like the kind of lettuce you get a whole head of at once

The one in the bottom right looks like it's saying "feed me!"

I wouldn't call that a failure... You seem like you're one tweak away from having lots of nice crisp lettuce

Maybe a bit more light? You can get led grow lights pretty cheaply if you shop around, you could try it on a couple plants to supplement the indirect light without raising the temperature much and test if it works