you need to prepare for the interview and have answers for officers questions. For example, if they ask you how long you will stay in Thailand, you need to say the exact amount of time (like “40 days”, no “ I don’t know yet” responses!). Where you go next, flight ticket out of country
You can extend for 7 days but you gonna pay 500 everyday of overstay. If they give you even 7 days extension, you can transfer your visa to another passport. I just did it this year but was not late as you.
But you will be ok, just will have to pay overstay. Go go!