VirtualBox Guest Additions won't install in Ubuntu Budgie

I’m trying to use Ubuntu Budgie on VirtualBox to get a feel for it before I go resetting my whole computer and dual booting. The problem is, I can’t use it full screen right now, and it runs quite slow because I can’t get Guest Additions to install. I installed and updated Budgie, and then I tried inserting the Guest Additions “CD” to the VM. Budgie recognizes it, and I could pull up an “autorun prompt” from the files program. I clicked “Run,” but nothing happens. I watched it for about 10 minutes before restarting Ubuntu Budgie and the entire VM, but still, no luck. Can anyone help me with this?

This should get you going: