Do you know for a fact how they felt about you? Unless you do, don't sweat it.
If that happened to me(being in the female's spot), I think it would be obvious that the guy was shy and nervous. Blushing says a lot also. It certianly doesn't say the person is being conceited and blowing you off.
Whoever introduced you to the girls should know how you feel, and the fact that you are shy. He/she should have let them know, or at least explained that to them if they took you walking away as a negative , blown off gesture.
Personally though, it's VERY easy to tell the difference between a guy who ducks out of the situation due to shyness etc,as compared to some egotistical dick.
I used to be really shy around guys. Eventually I just realized that by allowing myself to be scared and shy, it blew my chances with some wonderful people.
It takes time, that's for sure, but you have nothing to fear but fear itself. If they reject you, then so be it. You move on and find someone more deserving.