At two months, you are still very new to this and just starting to learn about your stoma... I'm four months into my colostomy now and I'm still learning.
Here's what I can tell you about size. When it was brand new, my stoma was so big that a bag barely fit even when cut to maximum size. Now it's about 32mm. The diameter shrank until it got to this size and hasn't changed from there.
That said, how far it sticks out above the skin changes almost daily. Sometimes it pokes out over an inch, other times it gets almost level with my skin. Sometimes it is at an angle, high on one side, low on the other. I have come to believe that this is related to how busy my colon is near the stoma, but I can't be certain.
As I understand it, there will be a natural variation in how much your stoma sticks out. If you're talking about diameter, I'm not sure what might cause that.
If there's no pain, fever, or other symptoms, you're probably safe to just discuss it on Tuesday - but I'd put in a call to my surgeon just to be sure.