Definitely install "Guest Additions." For that you will need to install the kernel headers in Ubuntu in the VM. This is an old Ubuntu forum thread, but it may help:
https://askubuntu.com/questions/2274...-virtualbox-vm
Try using the scaled view in the VM.
I have Ubuntu in a VM. It took me a while to get it to recognize the 1024x768 resolution that the VM was capable of. Unity did not want to cooperate. Eventually, I installed LXDE, adjusted the resolution in LXDE, then Unity because usable.
Afterthought:
I really really don't like Unity. It is annoying.