DataMn;353208 wroteComp is close, but as he said you have to take into account that there are less cards once each board pairs.
The true percentage is (10/42) (9/41) (8/40)... About 0.9%
Incidentally, his odds of scooping you we're 45.2%
And just to show you I'm more of a nit... It's were.. not we're.. :)