Your trim and C.G. is off.

A properly balanced and trimmed plane will not nose dive when given a firm forward toss.

Instead it will glide to the ground a good 15-25 feet or more.

That is why I suggest a more experienced flyer look it over. You have more than one thing wrong.

A nose dive indicates either a lot of weight in front, or too much nose down trim.

That it noses UP so quickly at launch tends to indicate that there is either too much weight towards the rear, or that the elevator is trimmed up too much, or the thrust angle is wrong on the motor.

An experienced eye will spot which of these seemingly conflicting problems is to blame.