Dear Whippett,
Yes many a true (American) English speaker realizes that the mother tongue has been debased across the pond. Whilst it is well known the, so called, "English" can not tell a z from an s, can not spell tire correctly, and have difficulty telling a car hood from a ladies cap, we still live in hope for your salvation.
Seriously though, the object of all those grammar rules, proper spellings, and writing styles, are to make your meaning clear as you tell your tale. Some would claim since the bulk of your readers are American you should humor them at the expense of your native dialect. I'm not such a purist. I would simply hope for consistency.
No one I know can properly proof read their own work since you tend to read what you meant to write rather than what is actually etched in photons. If you find the colonist to damn conflicted you might consider a more local source for proofing. These hallowed halls can still offer some tips on inspiration, style, plotting, point of view etc. Hopefully that can be of use to you.
Now to read the assignment.
Yours
Mad Lews