Looking down from shaft to prop you hold the impeller and spin the shaft clockwise, that's how the fins should be curved. The "arms" (fins) should be straight out before install. If they were already curved the impeller was used.
In reference to the prop, you need to get the motor into the upper part of the max recommended operating rpm with a "normal" load for you. According to iboats your motor is 4750-5250.