Will the GMAT Challenge Tests Help Me?

With around 3 weeks left for your preparation, I think your scores are decent enough. GMAT Club tests have questions more difficult as compared to actual tests. Except in few tests, you have scored more then 70%, which looks encouraging. Just keep moving with the challenges, and don't forget to review the explanations as well, you never know there could be a different approach to solve the same question.

Also, by now, you might already be knowing your week areas in quant, e.g. if its probability or co-ordinate geometry etc ?? For your weak areas, review the basic concepts from one of the books of your choice.

I would suggest you to attempt GMATPrep tests at regular intervals. You can try the same tests by resetting the test, believe me you'll not get repeated questions for atleast first 2-3 tries.