I agree with some of the above posts that Knewton is probably not much helpful for you at this stage. It helps you build good foundation and get to the level you are at, but for 45+ scores, you probably have some other options to consider. I am currently enrolled in Knewton. If
GMAT club tests didn't help you, look for some other advanced books. I don't know which books would help, may be Jeff Sackmann, Kaplan 800,
MGMAT Advanced question bank, just some options to consider.