The 60-Day GMAT Study Guide

Hi, I signed up for the Beat The GMAT 60 day study guide recently because I am scheduled to take the exam on May 10th. I am now on day 18, however, I have come to a self realization. When I took the first GMAC practice test on day 3, my baseline score was 420 (28Q, 20V). I want my real test score to be at least 630. I have since then studied each content in the daily emails and decided to give the Manhattan GMAT practice test a try today. This is when I realized I have forgotten to apply everything I've been learning for the past 18 days (specifically on the quantitative section because that is all I have been studying.) By question 10 on the test (quantitative section) I felt I was doing horrible so I exited the test.

I've been doing pretty decent on the problems in the OG 13 but it is not carrying over to when I randomly take a practice test. I think a bit of nerves kicks when I take a practice test in addition to not mastering each section well enough to keep up with the pace of the 60 day guide. Is there any advice that you can give to a person in my situation? Should I reschedule my test for a later date? Should I try classes in addition to self study? What would be the best way to tackle this exam.

I ask because all though I wanted to apply to some schools for an MS degree in the fall, I have no problem with waiting for the spring semester of next year.