I put my windshield in myself. The gasket and/or new glass did not quite fill the opening. I used RTV in the end to fill out the bottom corners and it looks and works fine. I understand that there is more than one maker of the gasket.
I have seen installations where the gasket stays within the groove around the outside creating a little crown to it. I have also seen them laying flat and extending past the groove on to the sheet metal. I don't know which is correct.
I found using a couple of the little articulated suction cups to be useful in the process. Part of the difficulty is keeping the glass centered. It is easy to get it too high or too low.
I am hoping that this post will get lots of comment so I can learn something here!