@maanyat periwal,
1. It doesn’t have inherent pitch stability
2. Looks like you don’t have a flight controller/ stabilisation system
3. No model can tolerate the extreme changes of CG you mention. Normally not more than a cm or so from the correct location (for a model of this size)
Not a suitable choice, by far, for entry into RC flying. (Neither is an A10 Warthog
)
If you look up ‘pitch stability’, you’ll get some insight into the problem.
Don’t let initial failures curb your enthusiasm. Keep at it.
But one has to learn to ride a bicycle before trying to ride a Bullet, no?
Best wishes
Iyer