Hi Grad0511

Don't get disappointed. You need to work hard towards it. I agree with Brent. See what is your target score and plan accordingly. There are millions of cases where students like you scored 400 odd on practice tests and improved dramatically by practising and scored 600+. Ensure that you are studying from the right material. for Quant basics, get hold of Manhattan GMAT strategy guides. If your basics are not strong, you cant do well on the exam because to answer every ques correctly in just 2 mins requires strong hold on basics as you cant expect to use hit and trial during the exam.
And practice alot from OG12 and the OG quant review. See which topics you are struggling with and ask your quant teacher to clarify concepts for u.

For verbal also go through the Manhattan guides and see where u need improvement. again focus alot on OG12 and OG verbal review

Do all that and give another test and see how much u improve and accordingly see when u want to appear for the exam.

Stay connected with BTG. Its an awesome forum. Look for inspirational success stories in BTG to boost your morale. There are alot of articles in BTG which talk about the typical mistakes students make while preparing for GMAT. Read all that may be you are making the same mistakes. See if u want to take a full course as attending classes does help. Anything else would be happy to help

Rgds
Tarun