Most people save their two GMATPrep tests, as these are the best simulators to the real thing. Right now, just get used to this website, find out what materials work best for you, and start studying!
A 700-plus score is certainly obtainable, but this requires time and hard work. I would say that, on average, one should study at least three solid months of preparation. As a junior, you have ample time. Use this to your advantage and please don't rush into this test!
Regarding books, Manhattan SC and Powerscore CR are the top choices for verbal. For quant, Manhattan's five math books have a loyal following. Kaplan is also popular as an all-in-one guidebook. And, of course, OG books are recommended.
For a very high math score, though, I urge you to look into
GMATClub Tests. Once you fully complete and review these tests, you will be 100 percent ready for quant.