Until you have the centered balance to not be thrown forward on your horse, I'd say never feel amatureish for pressing your hands on the horse's neck, or grabbing mane over the jumps until you stop getting thrown forward. I had to break my pride and grab mane when my trainer first started cranking up the jumps two years ago :)
When you go over the fence, try locking your elbows. It keeps you from falling forward. Also, really try to keep your shoulders back and really drop your heels right before the fence. This helps keep your upper body stay upright. Hope this helps!
Usually if you horse jumps quite big over the jumps and you're not used it to then, you need learn to balance and use your stomachs muscles over the jump. To strengthen your stomachs muscles you should work a lot with out using stirrups. Another thing is, putting a grid out and work your your position.
Most of the time when a rider falls on the horse's neck after jumping is that either he holds his reins toot tight and doesn't follow the horse's jump or that the horse made a too big jump.
In the first case, you have to be half seat to jump and when the horse starts to jump your hands have too follow his mouth movement. Don't look down, keep your eyes focused ahead or on the next fence. To begin you can hold the horse's mane or a collar you put on the neck.
In the second case, if the horse made a too big jump it's probably because the stride he took wasn't the good one or he didn't have enough impulsion.
To lead properly a horse to a jump, you must have a great impulsion until the last moment and keep your rein tight enough.