Manhattan GMAT Problem Set vs GMAT Questions

Hi,

I am completely lost. Since past 7 days I have put in about 50 hours on Quants itself. I was able to solve the problem sets but as soon as I opened GMAT club for some additional questions, I was shocked. I hardly could solve 1. Manhattan touches the fundamentals but the application is very very advance. Even the sub 600 level questions were difficult for me. I am completely broken.

Pls help what do I do? I have OG but I dont want to save it for a bit later.

Thanks