You’re correct, zero degrees means the North Celestial Pole is “up” when seeing your frame in landscape mode (we’ll assume 180 degrees is the same as 0 degrees, because the rectangular shape is just the same).
From there, the Position Angle “turns positive into the direction of the right ascension”, as defined by the IAU. This means the PA grows East of North - with the caveat that East is left of North in the sky (because we’re looking at the celestial sphere from the inside) as opposed to the Earth surface, where East is right of North because we are seeing the sphere from the outside.
To make this more confusing, some astronomy software got this backwards and now it’s very difficult for them to fix, because of the number of integrations they already have in place.
Here’s a topic where I explain the Position Angle in great detail: Position Angle / Rotation Angle - Is it backwards?
I hope this helps!