Hey,
Don't give up. Almost all complex problems can be solved by breaking down them into pieces and solving them one by one. Obviously not every one can score 750+ given the time constraints. But I firmly believe that anyone can score below that with combination of hard work, smart work and dedication.
First of all decide how much time do you have to take GMAT. Then decide a target score based on the colleges you planning to apply. Yesterday I attended a Stanford info session in which the adcom officer told me that they admitted students with a GMAT score of 500. The adcoms are not looking for brainiacs. If you have a good overall application then your GMAT score is not going to be a hindrance unless you apply to a school that wants to boost their GMAT scores. I "think" a safe score for you to apply to any top university is 650+. You can actually decide correctly as you know more about yourself than anyone.
Now coming back to the GMAT, start with Manhattan math guides. They are EXCELLENT. They helped me to go from 540 to 710 in GMAT prep tests in a span of three weeks. Don't rush to take tests. Master each sub topic one by one. Practice extensively. Do OG questions from each and every topic to check whether you are able to apply the learned concepts or not. Go through EACH and EVERY answer explanations in OG. Quant is something one can improve in a short span. In Verbal it is more difficult to do so but can be done. Try solving verbal questions logically basing on their meaning rather than try to apply thousands of grammatical rules. And see how it goes. Think of it like this: What's the fun if you score 750 in the first mock test you take? What will you learn from it? GMAT is one of the great journeys you will undertake in your life.
Most importantly GMAT is just a test and it's not perfect. Move on if you don't like it but before that take a GENUINE crack at it. Nelson Mandela or Gandhi might not crack the GMAT, but they are great leaders. If you have the dedication in you to become a leader/manager/problem solver, you will become one with or without GMAT.
All the best. Hoping to follow your progress.
Thanks,
Prodizy