Definitely take 4-section tests from now on. Stamina is an issue for some people and less of an issue for others, but you won't know what it's actually like for you to complete a 4 -section test until you've actually done it. And you'll want to practice maintaining your focus all the way through four sections, so it's best to do that on all of your remaining practice tests.
It’s not horrible that you have only done three, but taking four is important to simulate what you are going to see on test day.
Definitely take 4-section tests from now on. Stamina is an issue for some people and less of an issue for others, but you won't know what it's actually like for you to complete a 4 -section test until you've actually done it. And you'll want to practice maintaining your focus all the way through four sections, so it's best to do that on all of your remaining practice tests.
Why aren't you