Hey, I tried to reproduce this issue but everything seems to be working fine for me using Unity 2020.3.9f1 and the 2020.2 template. When you say it's not resizing, what's the behaviour you're seeing?
I was able to reproduce the "no dimensions provided or detected" issue, but that appears to be a bug in itch.io itself: the same thing currently happens when using the default unity templates. You may be able to report this to their support for more info.