Preflop
When people limp into your BB instead of raising, they allow you to see a free flop, which is the whole reason, why limping is not recommended in non-ante cash games. This also mean, that raising need to be higher EV than seeing a free flop. And when you raise a hand like this, what are you realistically hoping for? The whole reason, people limp, is to be able to see a cheap flop. So is there any reason to think, that BTN will limp and then fold for 2,5BB more?
Its almost like, you are helping BTN to play better, when you make this small raise. And of course the goal in poker is to induce mistakes from our opponents, not to help them correct their mistakes. Then you could go larger like 5-6BB, and maybe now you would start to see some folds from BTN. But you would also bloat the pot even more, when he call, and you are still out of position with a bad hand. So for me taking a free flop is vastly superior, and I would only be raising here for value with
hands much stronger than A6. Maybe AT+, A9s, KQ, KJs, 88+ or something like that.
Flop
You could C-bet here, since its a dry K high flop. But you missed completely, so its not like, checking is a huge mistake.
Turn
I think, a delayed C-bet is ok, but I dont think, you need to go so big. Its mostly to clean up
equity, and half pot or even less should get that done.
River
I would also not bet this card, since your line is not representing, that you have a 7 in your hand. And as it turned out, you also had showdown value. Your opponent is the one, who should probably have bluffed at some point in the hand, not you.