On a single screen, I press F12 to open yakuake and covers all screen. If I connect a second screen, I press F12 and yakuke only covers 1/4, sorry maybe a little more, but not all of the screen. I'm not sure if this is a yakuake bug or not because the only program that does this is yakuake, all others are working fine.
Turns out the problem was with the screen scale set in System Settings > Displays. It was set to 1.2 causing yakuake to have this weird behavior.