The prop can be bad did you hit any rocks or anything that could have scuffed the blade?
also make sure you are getting 100% full throttle turn the boat on and on the radio push the throttle trim up just intile you here the motor starting to make nose then turn down the trim just far enough to stop power to the motor.
Also one last thing try the boat with the battery placed more tawards the rear and then try it with the battery more tarwards the front and see how she goes.... also a boat wont get on plane if there is weeds in the pond the pond needs to be clear of weeds andy little weed caught on the boats turn fin or prop will slow it down so much that it won't get on plane.