Why ρωτα and not ρωτε?
Because ρωτάω belongs to the -άω declension, not to -ω or -ώ - these have a short form imperative in -α as well as the regular one in -ε which would be ρώτησε.
Similarly, "Love thy neighbour" is usually αγάπα τον πλησίον σου but could be αγάπησε; Look! can be κοίτα! or κοίταξε! etc.
Both are accepted as correct. If yours wasn't accept you should have made a "My sentence should be accepted." at the bottom of the exercis page, before posting here.
Do that every time a sentence is not accepted and you think it should be. Be sure to comment here so we find your REport.