Getting that first flight to trim the plane can be a problem if it is way out. (Sounds like you needed a bit of up trim on the elevator.) When you get it back after that flight look carefully at the elevator. If you have down trim on the elevator you are set up for a crash on the next launch. It is almost certain that if you have down trim you will crash on the next launch unless you correct it to neutral or slight up trim. You can correct a down trimmed elevator by moving both ailerons down. You have to experiment to find out how much.

Planes that take off from their own wheels aren't bothered by this as the pilot gives up elevator just as the plane lifts off. ,

Some people use an overhand launch, some people use underhand, but I have never seen a launching tool used around here.