I know you won't want to hear this but pull it back harder.
The first couple of times are really hard but once you figure out how much effort to expend, it does get easier.
First time I tried it I was in the store with the salesman and we spent 10 minutes trying to get the thing to move. I was convinced it was broke.
It is NOT something that is convenient in the deer woods.
I have seen an alteration made to them by welding a pull ring on the back and if you are going to use it for hunting and don't mind altering it, that might be the way to go.