@Stephen ***********
The 3-months visa validity is not the same as the duration of the stay permit you will receive upon entry.
The visa is valid to use for one entry (single entry) for three months, starting from its issue date. You will get stamped in for 60 days.
You can buy a 30-days touristic extension on Immigration for 1900.- Baht for each entry, but only once. . Before these are up, you need to exit Thailand and you might be able to get stamped in on a visa-exempt entry for 60 days (at least at the moment).
But be aware that each visa-exempt entry is at the sole discretion of a border official.
Best is to be prepared to show the three proofs: 20,000 THB or equivalent in cash, a booked accomodation for the next few nights and an onward travel proof out of Thailand within these 60 days
You would be better off with a multi-entry 6-months tourist visa. This visa will be a better guarantee to enjoy a 6-months stay