bad play?

I get pocket 10's with someone else raising about $4 in a .25-.50 game i play. someone after me goes all in for a total of about $6.50. we both the initial agressor and i both call the extra $2 and the flop comes J, 10, 6. i'm thinking i'm golden and notice they are all the same s00t. The initial agressor raises $4 again and this is where i think i went wrong. instead of re-raising with my set and maybe making him think i already hit the flush i just called. I always have a good read on this kid and know he's holding AQ or AK and he knows when i reraise hard that i have a made hand, but i didnt even have a diamond and we were both stacked at about $50+ so i didnt want to take a risk. the turn comes and puts that dreaded 4th diamond out. now i know i'm beat. The agressor bets out $10. now i start doing some math....

preflop the pot was 6+6+6 after flop 4+4 so there's roughly $28 in the pot. now on the river i can either catch another 10 (unlikely) or pair the board for a boat and destroy this flush. so i figure i have 7 outs with and about 25 cards gone from the deck. he's betting 1/3 of the pot and i have just about 1/3 of the deck as outs. should i have called the $10? i ended up calling the $10 and the river was another diamond so i folded face up showing him he was destroyed if the board paired.

was this just a really bad play, bad luck, or are my way of calculating pot odds gorilla math :shock:

7 outs with one card to come = 15% to make your hand.