How can i fix my Twin cut TC102?

I have just put a new deck on my Twin Cut TC102 (like castle garden) and when i reasembled it, it is not mowing properly. It is leaving a gap in the middle, the grass left is being hit but not being cut properly. I did sharpen the blades before reassembly but am not sure if I done it properly. Does any one have any ideas as to what i can do.