Any idea why?

 

The top won't fold completely if the elastic bands located roughly over your head are worn out, and keep the cover from closing. If you keep opening and closing it to get it to fold completely instead of replacing the straps, the top will eventually tear. I'll dig up the short write-up I did on replacing the straps.

 

Here's information on replacing the straps:

https://my350z.com/forum/350z-roadst...-tutorial.html

Pull on them with the top up/closed and see if they're slack, if so, that's probably your problem.

 

there is a bar right on top of your head when the top is closed that rolls forward when closing and rolls backwards when opening. your is actually stuck forward and your 2 inches you see in your picture is the space that bar is taking. So just help it go backwards when opening the top. The bar is actually the one that has the hand thing to hold on to.
let me know if it helped. No need to replace anything.