Welcome to ZA, Grey!!
I moved you over to the right section.
To answer your question, you do need 5 stars to get a Giant Panda. Unfortunately that still doesn't guarantee you'll get one in the extra slots that become available when you reach 5 stars. It is still random whether a Giant Panda will fill a slot.
What you will need to do is keep rejecting all the other animals you don't want, so another choice can pop in, and eventually you will get a Giant Panda. Keep in mind that you have to BE at 5 stars, not just have reached 5 stars, so anytime you dip back to 4.5 stars you will not get the Giant Panda as an adoptable option.