Hi Nina, I understand how sad you might be feeling right now. But dnt loose hope. There are ample stories of increase in 150-200 points with good prep. All you need is VERY structured and disciplined approach which begins with identifying your weak areas. Just going through books will not guarantee your scores. You have to improve on your weak areas and the improvement should be result oriented and quantifiable. For example, say your accuracy in sentence correction is 70% (however accuracy is not the best method to gauge the performance but lets assume so for understanding), it may be that you get all pronoun related questions right and all modifier related questions wrong. You have to identify where are you going wrong and why are you going wrong and how can you improve. Studying for 3 more months can yield desired returns but you really have to keep on questioning your preparation and quantifying the results.
I hope I am making sense!
All the best!!