hey ....
i guess the GMP will be usefull ONLY if you are very confident about the course that you have have covered .......otherwise it may even lead to confusion!!!!!!
i suggest that you go through what you have already covered once again i.e revise ............and if in any topic u feel very confident then you can handpick those problems from GMP .......
personally i feel that giving more and more tests helps one even better during the last days ..... but you know you still have some time before that so i'll suggest that you revise .......otherwise there are books u can refer to like arihant series ....., there are brilliants YG-files etc
........keep it cooollll.....