So you just had 4 months in Thailand with one single entry tourist visa one 30 day extension and one 30 day visa exempt by doing a boarder bounce.
If you’re going back to your home country for 2 months you should apply for a multiple entry tourist visa that you can get nearly 9 months out of if used correctly.
There is always a chance a immigration officer could stop you on any entry and ask you for proof of funds accommodation and onward travel.
The officer may have stamped you incorrectly, but It’s your responsibility to check your passport entry stamps. If you had you could have had it corrected free of charge.
The bus takes about 10 minuets to cross the boarder but it’s a dirt road that’s a bit up and down, not sure of actual distance.
It crosses stops by a duty free shop they take your passport get stamps and pay the fee to enter Myanmar, then drive you back. Fee is probably $10 so the rest of the 960.- is for the bus ride.
I did it a couple of months ago. Not a bad trip just 3 and half hours from BKK.