Don't worry too much about it! It happens to all of us.
I know that I have recited the same prayer 3 or 4 times because I got distracted half way through, and started over, ... and over.... and over!
Best advice I can give...is relax for a bit before you start in on your prayers. Quiet your mind. Let the distractions of the world move to the deep recesses of your mind.
Once your mind is settled, then begin....otherwise, you will get distracted. "Oh, that bill was due today! Darn! Oh! I forgot to feed the cat!" etc.
Hang in there!