Let me clear this up for you, and sorry for some of the comments.
Your embassy has nothing to do with Thai visas. You need to go to a Thai Immigration office inside Thailand (there's one in every province) and apply for a 30 day extension. You can do this one time per entry.
The cost is 1900 baht, you need your passport, a picture, a TM30, and copies of your passport.
Single entry tourist visas are valid for 90 days from the date they're issued. If you enter on the first day or the last day it's valid for, you'll be stamped in for 60 days.