@Lê *****
Suggest you ask a Bangkok border run service company to take you to the Thai border AND bounce out and re-enter to get a NEW Visa Exempt Entry into Thailand... 45 days if done by March 31. From April 1 it's 30 days Visa Exempt Entry. Plus you get One 30 day extension of stay at Thai immigration office for 1900 Thai baht.
Google Bangkok Border Run.