Welcome to the site!
Wow, forty pages in slightly over a week is an impressive writing speed. As far as I can tell from your post and what you have finished from your game so far, your English isn't a problem - there are native English speakers on this site that publish games much, much worse than yours in terms of grammar, spelling, and coherency.
Like everyone else said, getting a proofreader/coauthor is your best bet - there's a thread for people who've offered to do editing and play-testing here. You can also request your storygame to be reviewed here.
Alternatively, just make a thread in the 'Writing Workshop' forum asking for help.
Hope enjoy your time on this site and make a great storygame while you're here!