Just keeps getting better

I thought the two out suckouts were bad. So I am in the first hand at a 25/NL table. I get pocket 9s. The flop is 578 2 clubs, so I got overpair, backdoor flush, and straight draw. An idiot goes all in and I KNOW I HAVE HIM BEAT. Why? Because I am better than you and I know these things.. So anyway, I call his $36 bet with my measly $20 and he flips over 76. Not bad. I have his ass. So Middle pair is so worth your entire stack. Sooooo anyways, the 6 on the turn gives me the straight. Cool. The 6 on the river however gives him the boat. Not cool. What exactly do I have to do to win again?