Translation: My hair is short enough my real ears show. The fact that wearing cat ears for a costume would create the appearance of four ears irritates me greatly. What are some possible solutions to this dilemma?
You didn't link the character you are playing, therefore it is difficult to offer an appropriate solution, but generalities may be made..
It might be possible to wear a scarf or headband that hides your natural ears (And I personally find quite fetching with au naturale curl).
It might be possible to wear a hat or stocking cap of some sort that will hide your natural ears, and attach the cat ears to the hat instead of your head.