@Frederick *****
okay, anyone can be asked for proof of onward travel when they fly into the country AND they can be denied entry without it, so consider yourself lucky they let you book onward travel and stamped you into the country.
You will be able to get a 30 day extension at the immigration office on the entry you're on for 1900baht.
As far as an ED visa, It's not that hard to do, you find a school in the area of thailand where you live that offers ED visa support, enroll, pay your tuition, get your paperwork from them and go to a thai consulate in a nearby country and get a 90 day single entry ED visa. you get stamped in for 90 days and then when that runs down the school gives you paperwork to go to the immigration office and get a 90 day extension. You do that for the length of the course..