That's great news and well done on taking all the photos too - multi talented!
You're right about that Amazon ranking - it does mislead, but until you get royalty statements through which are usually only once or twice a year that's really the only yard stick you have.
Make sure you organise some local book-signings and/or readings. Get yourself out there as much as possible. Think of as many angles as possible to help get you some free advertising from the media. Check out any Shetland related websites and get reciprocal links to them in addition to trying to get a mention on them all.
In a lot of ways the marketing of the book is harder than the writing of it. But it can be very rewarding. I have shamelessly marketed my books for 2 years now. At least once a month I have a book-signing in a different store on top of appearances at schools, networking and literary events.
You've just got to keep plugging away.
All the best,