Look at the bright side. Could have been a 9 on the turn and a river 9.
A paired board bigger than your hole cards is always dangerous. You did tell us u raised the 20.40 pot bet to 50, and the push put u all-in at $120.
I think most here have said your play was right and it was just a cooler. If u lose, simply reload. I'm an old time limit player, so my take is a little different. I would have called the 20.40 and let it go at that.
Once villain pushed, I think I would have sensed I was in trouble. No shock about the muck button. Just curious - you didn't tell us if you showed or mucked ... ??
Why would I have just called the 20.40 pot bet? Stated that earlier. Facing a board pair bigger than my own. Even if villain had K,x in the hole, he already has me set over 2 pair and I have the low end. Any matching card to his 'x' in the hole also gives him a bigger boat 'if' I hit mine, as the 9 did on the river. Even a K,9 for the villain was quite possible.
Just me, but I would say u got outplayed. A check-around on the paired board turn = caution. Calling the pot bet, with one left to act, might have been a better play. Maybe SB had a K,x as well. Either hand could have me beat. If I call the bet and SB folds (which he did), it wasn't him. End of story, I win ~$65 or lose $30. Over-value of a weak boat cost $120.
With 2 players still in the hand, it's also quite possible that BOTH villains had u beat. One with a K,6 and one with K,7 (or even K,9). Not an unlikely scenario. Just my thoughts on playing weak boats into a paired brick board.