In magic when I use devices to create a layout of an NMOS, the gates are all alternate and do not seem to come at one side, is there a way to resolve this??

From your message its not clear what you mean

This gate contact being alternate in nature.

The contacts alternate sides when the device is too narrow for the gate contacts to be placed next to each other without causing a DRC violation. Note that you can always edit the parameterized cell and modify the layout any way you want to. Just be advised that whenever you press the "Okay" button in the parameterized device generator GUI window, it will erase any edits you made and redraw it the way it wants to. Otherwise, the cell will be saved with the edits.

Okay, let me experiment with this. Thank you