Booked to come thailand miscalculation means im in thailand for 61 days tourist visa is for 60 days can i leave after say 58 days and come back in by land and get a 30 day visa on arrival.

Yes, (but it is not a "Visa on Arrival"), or you can go to immigration and get a 30 day extension of your original 60 day entry.

• If you're leaving by air on day 61 you don't need to do anything. They don't charge for a 1 day overstay at the Bangkok airports, because your mistake is common.
• You could apply for a 30 day extension at immigration for 1,900 baht.
• You could do a border hop by land and you'll get 15 days unless you're from a G7 country in which case you'll get 30 days. It's not visa on arrival. 

For a couple of days I wouldn't bother, just leave one day late.

 

I've done it before.