Maybe you didn't type the " ' " behind po, Elen-ka?
It is important to type "un po' " instead of " un po" (mind the ' ) Because po' is short for poco, and the ' comes instead of "the missing part" of poco. And "po" without ' definitely is an error. One of the biggest you can make in italian spelling...because of reason I just mentioned.... :)
(....and well....i am just repeating things I've read in another comment somewhere in duolingo...)