@Les***
I highly doubt you got stamped in for 90 days at the immigration office in Samut Songkram on a Non-B visa without actually having a Non-B visa IN your passport :O
(and I'm of the mind that it's IN your passport somewhere) but. . . .
Be that as it may, you cannot use this entry to get an extension at another company because the school that sponsored you for this one is written on your 90 day admitted until stamp.
you're gonna hafta exit the country and either come back in on a tourist visa, then apply for a new Non-B visa like you did this time OR get a 90 day single entry Non-B from the thai consulate in another country.