@Andrew *******
That visa is a single entry <- meaning the second you come in and get stamped in for 90 days the visa is done.
As David correctly stated, you come in you get stamped in for 90 days, and you can get two 90 day extensions at the immigration office. You don't need to leave at all during that time.
Now what happens after that, no one knows because right now the borders are closed and you ain't gonna border bounce like you could before this covid shit show started.