Need beginner jumping help!

I'm new to jumping, I only started about a year ago. My trainer says that, when I'm working on my two-point at the walk/trot, I look really good. But usually when I go over jumps, I either get in front or behind the movement (these are only small cross rails & poles 18 in. Off the ground!) Then, I get the breath knocked out of me!

I almost fell off over some grids once, and I've fallen off twice before. I'm SO freaked out now, that we've backed off to just walking/trotting.
I'm sure that some of you here are jumping 4 feet easy and you think I'm crazy to be freaked out over 1 feet parallels, but I'm hoping that you can remember some of the tips & techniques that you learned when you first started!
Thanks!

You need to go back a step and gain a more secure seat. I don't think that you are ready to jump, yet. IMO, you need time riding without stirrups so that you can feel the horse's motion and be able to be relaxed while following it.

^ Great advice, I would do lots of no stirrup work. Walking/trotting, posting and sitting trot. Once you are comfortable with that I would work on your two point without sirrups. But you need to be comfortable with w/t before you can canter. Which means you have to be really solid and comfortable with canter before you should jump.

To me, it seems like you need more confidence in jumping. You should start with simple balance activities, like Around the world at a walk or trot, or using no stirrups. Bareback work would also help for going over jumps, since it helps with leg muscles. I used to be in the same position as you, so I know how it feels. When you are heading for a jump, you should keep your head up and focus on where you are heading. If you are getting left behind, you should go into a two-point or three-point a few strides before the jump, so once you reach the jump you will already be out of the saddle. Counting strides also helps alot. Counting a simple 1,2,3,4 in your head at a trot will help, or a 1,2,3,4,5,6 for cantering will help you with getting into two-point before the horse takes off.

Don't worry about how high you're jumping, it's the quality of your jumping. I'd rather be jumping small with precision and straight lines than a messy and dangerous higher course.

Second of all, there are lots of exercises to improve your seat, as mentioned above flatwork without stirrups.
An exercise for you getting used to jumping with the horse is a two point in trot over poles before and after. So as you come around the corner, go into two point, keep your eyes up and go with the horse and see if you can balance yourself. Make sure when you are jumping normally don't two point before the jump unless instructed, just in case your horse refuses and you do what I call the "catapult" and go flying over your horses head.

I really understand the whole getting left behind etc.. My horse is a careful jumper and if his distances aren't right coming into the jump he will most likely take off very early (and very high) over the jump. Even my instructor said, it's just him and you'll be able to get a better seat and a position in time and get used to him. You can then understand when he's going to take of early.

You can't rush jumping, take your time and ask your trainer to see what exercises you can do to improve your seat.