Hey guys just got can of plexis! HELP

[nautiquelfe]

As above i just received can of plexis today and am badly in need of cleaning my neglected rear window. I have read many posts on the use of the plexis and am confident in applying it safely. However my interior side of window is very gritty. It seems previos owner drove w/ windows down top up and the window is so dirty. You can see the granuals. I am hesitant to clean interior to harshly for fear of scratching the plastic badly. I thought of using some sort of foam cleaner in hopes of lifting some of the debris off the surface. I would love any suggestions. I would love to clean today but feel like i would be better off waiting for proper support on the issue. It's so nice having a forum full of experienced people to turn to when doubt creeps in my head. Thanks for past, present, and future help, hopefully i can contribute as others have for me.