The bet on the flop - pot size - was alright although 1/2 to 2/3 would also have been good and cheaper when your testing your hand vs the rest of the table. OK, you bet pot size and got two callers - what do you do now before the turn card is up?
Answer - ask yourself 2 questions!
1. What do they have that would justify a call to my bet?
2. What can I beat?
With a flop of 3 diamonds, answers to your first question should include a made flush and a flush draw probably to the

or

. Other posibilities are another K pair, 2 pair, trips and a not too likely 6 hi str8 draw.
Answer to your 2nd question should have be K-9 without a diamond or worse - i.e 2nd pair.
Now ask yourself a 3rd question - do the possible hands in Q1 and the hands I can beat in Q2 make an all-in move that makes any sense?
Answer Q3 yourself but pls share it with us..