Im not sure what happen during your install, but if i remember correctly... this happened to me one time when I booted the 3.3 install USB via UEFI. I believe I got different menu options to install. At the top of the list wast a generic "install" while towards the bottom were the normal "insall zentyal(delete all) or install zentyal (expert)" -i think. When i chose the generic install option it installed ubuntu only, just like in your case.
Anyway... I dont see why you shouldnt be able to
apt-get the zentyal packages and continue from there. Here is the official doc from ubuntu describing all the packages u can install and how to direct to the zentyal repository for all packages avail.
https://help.ubuntu.com/12.04/serverguide/zentyal.htmlOtherwise, you could try a vanilla install and be sure you are selecting an install option including zentyal in the label, or try expert install, if you havent already. Good Luck!