I had similar scores when I started to prepare for GMAT.

GMATPrep : 560, 580, retake : 550 , 620.

Kaplan : 530, 520

Princeton: 520, 570

I would suggest the same as what I did: (It may not be the best solution but it has helped me a lot)

1. Instead of rushing and taking more and more tests. Try to go slowly building solid foundation.

2. Start with Manhattan SC and maintain

error log. (Do SC for at least 4-5 days) Solve as many problems as you can.

After 5 days review your mistakes from

error log and mark the repeated one's with RED (weakness).

3.

Powerscore CR bible : try to read each and every details. Solve as many problems as you can after that for 4-5 days.

4. Do the same for Maths: Instead of rushing to difficult questions try to solve simple questions to build foundation.

5. For RC : I need to work on it . So no suggestions. Practice is the key.

After this try to take one test to check your progress.

I repeat: don't just rush to take test.

_________________

GMAT Club Error Log V3.0 - with Timer

GMAT Club Error Log

Spoilt Error Log V0.0.9 - with Timer

Awesome Error Log - By Spoilt and Trianglock