So then it is not really antimatter in the sense that it is completely opposite?

So antimatter still has a positive mass?

In my limited understanding, antimatter just means the particles have the opposite charge of normal matter. All other attributes are not part of the definition of antimatter.

Charge isn't the right word, although I'm not sure what the right word is. Otherwise you've got it right.

No, charge is the right word. But i was wrong about charge being the only difference, apparently antimatter's "parity" and "time" are also opposite of normal matter. Whatever that means.

https://en.m.wikipedia.org/wiki/Antimatter

The Feynman–Stueckelberg interpretation states that antimatter and antiparticles are regular particles traveling backward in time.[18]

So just like in Tenet?