Can I enter Thailand as a student without a return ticket?

You will be detained without a return ticket

If you have all your paid for school receipts you'll be fine, as it does take them a few weeks to get the ministry of education approvals back to take to immigration, as you are under a different classification by enrolling in a regular university, so it takes longer. The ED Plus is a good option.

I find it interesting that everyone attempting to get around the entry requirements that have been in place, but until recently, still asking what their chances are... being that the OP is looking to get an ED visa.

To me, I think the better question is, what happens exactly when a person gets denied. It's not pretty, for sure.

There's a workable solution; a ticket that a person can rebook for a different date, at any point in time... that's a lot cheaper than being denied and sent back to their original departure country, and possibly experiencing immigration detainment while waiting for the return flight... then again that's just me.

You will probably be fine entering Thailand IF your airline will let you fly, check with them