PokerStars No-Limit Hold'em Tourney, Big Blind is t100 (8 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

BB (t3435)
UTG (t1830)
UTG+1 (t1145)
Hero (t1240)
MP2 (t1150)
CO (t1615)
Button (t1655)
SB (t1430)

Preflop: Hero is MP1 with 5, 5.
UTG calls t100, 1 fold, Hero raises to t300, 5 folds, UTG calls t200.

Flop: (t750) 5, K, 7 (2 players)
UTG bets t1530 (All-In), Hero calls t940 (All-In).

Turn: (t3220) K (2 players, 2 all-in)

River: (t3220) T (2 players, 2 all-in)

Final Pot: t2630

Stupid? Obviously I got majorly lucky on the flop.

If you have QQ+ then ok, but not with 55.

Short answer: yes.

Here's a question: what was your plan for the rest of the hand after making that raise? The raise isn't big enough to give you a good chance of taking the pot PF, so what were you planning to do on the flop? Say that card was a 2c instead of a 5 and UTG checks to you. The pot is 750 and you only have 900 left - are you going to CB for half your stack at that point? Check behind and basically give up on the hand? Or put the rest of your chips in against a player that has you well covered with a pair of 5's and 2 overcards (one of them very dangerous) on the flop?

Your only raising option with 55 there is to push, but the better play is to just throw it away and wait for a better spot, IMO.

QFT

Yes. Push or fold with 12 BB left, unless as mentioned above you're sitting on something good like QQ-AA and want a big stack to re-pop.

It's a shame to throw away a pp, but limping isn't an option here.

Like everyone else said, raising to 300 here is prettty bad.

I think i'd fold here PF.