I think I'm just doing something wrong here. I looked around here and found several issues pertaining to scaling and mirroring but I couldn't find one that I felt was applicable to me.
Basically I'm learning Blender for the first time through an online course. They had us cut one of our models in two, and then apply the mirror modifier.
This works fine, but then I try to scale out the top ring of my model by three units, and got some weird results.
The top one has a mirror modifier with the top ring scaled out three units and you can see how it's created this oval shape.
The bottom one is the same shape as above pre-scaling. I applied the mirror modifier so it became a full shape again, and then selected the top ring and scaled it out again by three units, and it presents how I expected the mirror modifier above to.. So what am I missing?
You can find my .blend file here: https://drive.google.com/file/d/1rSZ_AsEMzvMw5ZtUSTj-y5NMIoj8Fer0/view?usp=sharing