As the previous poster mentioned, you really need to take a diagnostic to get a true sense of your scoring potential. You are scoring at 70% on the OG problems, but it really depends on where those problems lie in the OG (the problems become increasingly difficult as you go along as you probably noticed). You also need to remember that the CAT is an adaptive test, so you can't judge your success by the number of problems you get correct but rather on which problems you are getting right.
There are lots of diagnostic tests available (here is the
MGMAT exam page
https://www.manhattangmat.com/free-gmat. ... paign=home), but at some point before taking the real test you will need to take a practice GMAT from the GMAC (the makers of the GMAT). You can get access those exams here:
https://www.mba.com/the-gmat/download-fr ... tware.aspx.
Best of luck!
KW