I'm not a Linux expert either but I've been using it as an alternative to MS Windows for a few years now.
Linux is structured like the early versions of MS. There is the kernel which gets updated now and then like MSDos 5,6, etc. Then XWindows is built on top of that as was Windows 95/98/XP.
Quite a bit of work goes into the seperate Desktop Versions, XFCE, KDE, GNOME. I suspect the version of Gnome you have is not compatible with the XWindows implementation on RPi. It think the reason Gnome wasn't chosen is it takes more resources than the RPi is designed to deliver.
I'd really like the RPi to replace a laptop by running Gnome and OpenOffice but realistically there would need to be a few changes. On the other hand I have a HP Notebook with a 1GHz VIA processor that happily runs Mint Debian with Gnome and runs the full suite of programmes. The main difference is the amount of memory available. Another point. There has been almost 20 years to optimise Linux for Intel processors. The implementation for ARM processors is new and may not be optimal yet.
I'm sorry but I can't tell you how to fix it. Not very helpful but maybe someone knows more than me. It might help if you say where you downloaded the Gnome3 from.
Greetings to Germany