Ubuntu installs but won't boot (reinstall prompt every time i start up)

Completely new to Ubuntu and wanted to give it a go so tried to install it on my Macbook Air 6,1

Installed from a USB device using Universal USB Installer and removed my previous OS. It prompted me to restart following installation but on restart it just gives me the menu with "try Ubuntu" "install Ubuntu" etc.

When i attempted to install again it recognised the Ubuntu OS as being installed (it gave me the option to install Ubuntu alongside the Ubuntu i had already installed)

I tried using Boot Repair and once again it seemed to be successful but once again the same thing occured when i rebooted the computer. (Boot-repair pastebin: paste.ubuntu.com/12386688)

If i remove the USB the computer doesnt recognise any OS at all so wont load up which suggest to me that i've installed it onto the flash drive or something but i can't work out how to fix it.

Any help is massively appreciated :)