@Will ******
seeing as this is only the FIRST time you're going to bounce to get a 90 day entry stamp AND not knowing if your immigration office allows one 60 day extension per entry OR one 60 day extension per visa I'd say just bounce out and back tomorrow.
Sounds like you were going to use a visa run service anyway, so you will be okay getting to the border.
Believe me you're not the first foreigner in the history of thailand to border bounce with a one day overstay.
I would definitely start paying attention to what you're doing, AND know that you don't need to wring every single one of the 90 days you get on an entry stamp out before you bounce to the border. A few days before is fine too, so you don't run into situations like this...