Can I self prepare for gmat?

I started preparing for the test 2 months ago. I completed the manhattan books and had started solving questions from kaplan’s question bank and gmatclub. IMO the books are not preparing me for the advance concepts.

I tried to take a 21 question mock on the kaplan question builder consisting of just medium and hard questions…it took me 1 hour to solve with just 57% accuracy.

This was my 1st trial of hard questions but I feel I need to prepare more to tackle these questions. Can someone suggest how to prepare for these tough concepts and question.

Also let me know if I’m panicking too much and practicing more will relieve this issue!