@Lau***
, sounds totally fine, you're allowed to be here until Oct 6th. I think what your friend was confused about is a single entry Non-Immigrant Visa is good for 90 days from the date it's issued meaning you have 90 days to enter thailand and get a 90 day stamp. You could have entered thailand on the "enter before" date which is stamped on the visa itself and you would still be stamped into thailand for 90 days.
I would get a new passport between now and Oct 6th when you need to be outta the country though or you're not gonna get a SETV from any thai consulate..