disastrous GMAT 460 (Q38, V17)

Hello everybody,
Yesterday I took my first official GMAT test, and I scored only 460 (Q38, V17).
I studied only 1 month for the test( I only studied from the Gmat general official guide), and I already knew that I would have been very difficult to get a good score( I was aiming for at least 500, but ideally 600+).
The problem is, until the bay before the exam I was standing around Q30-33 and V22-27 almost in every mock I took, while in the official exams the points were completely different( better quant and much lower verbal).
I don't know how that's possible, even in the first mock exam I took ( without knowing how the gmat works) I scored V22, and I never scored below V22 during all the month of preparation.
I'm disappointed because with a verbal of 22 I could have passed the test with a score of 500( which is the minimum required for one of the masters I want to apply for).
Another problem is that I have to retake the test again, and score at least 500, but I don't know when to take it, the options are: in 2-3 weeks from today, studying around 15-20 hours per week, ore in July (studying only 5-8 hours per week).
In every case I cannot study that much for it because as I said in another post I have to graduate in july from my bachelor degree, so I have to take 3 exams+bachelor thesis.
To be honest, it would be better for me to retake the test in 20 days from today, since I still have the fresh concepts, however I need to be "sure" that I can pass it with at least 500.
About that, I was thinking to buy another book/books about math, so that I can "ensure" a quant score of minimum 36-37, as in general I always scored 22 or above in verbal( except for the exam). Could you suggest me some good books that could help me improve my quantitative score? However, I cannot spend that much for the books, I was thinking for something about 80-100 dollars max, maybe something even cheaper.
I accept advices about everything( strategies, books etc..).
Thank you in advance for your help!