Well most of the programs/sites automatically add the miners fee in there.  It is usually .0001 or .0005. BTC.  
And nope, you can't cancel it once it's sent.  

I think maybe they can possibly "bounce back" to you if they never get confirmed somehow but I don't even know if this is the case.

You are probably ok and it will go through today or in the next few days.  It only took a few extra hours with mine that I didn't have a fee on.