Ruben,
Sorry to hear that. But keep the motivation, you can definitely improve your score. Look at me, I've taken the gmat several times, I've done the same thing as you : first test 570, 2nd test : 500!

But after some time I just got 620. I am sure you can get a better score.
I think that the key of he gmat is to understand the concepts. Of course you need practicing but the second time i took the GMAt I had been practicing like crazy ! I mean doing as many exercices as I could...and it was a big failure : 500
One year later I just can say that I've studied less time than before for this last test but my score is better. However I try to understand all the problems like : distance/Speed, working hours, prob with balls, C and P, ...if you understand WHY you do the operations, you will feel more relaxed when you see a problem.
Another big issue is I think the Ds and PS realted to number properties and the algebra that, in my opinion, represent today most of the question. Without revealing the questions, what problem did you face ? Did you have timing issue or not ?