Multi entry B, last entry stamp good till June 7, Visa expires December. Can I now stay until July 31 without doing anything ?

It's my first time in many years with a Multi-Entry B visa like this. My first 90 days are up this week. I should be able to simply do a border run, cross in and out of the country (Mae Sai), and get stamped in again, correct? No need to go to Immigration in my Chiang Mai, right? And no need for a re-entry permit either, correct? As far as I understand, there is no 90-day reporting for this one, just the exiting and re-entering the country.