They might not realize that you're gay, and they might not mean that you need to wear skirts and such.

Western society has come a long way in regards to women being accepted in all manner of fashions. It is no longer a big deal if a woman wants to have very short hair, wear jeans and t-shirts, or never touch makeup. Only ignorant people are going to look at a woman with short hair and jeans and think, "She must be a butch lesbian." Part of this is also due to doing away with stereotypes towards homosexual people, as well.

So chances are that they just meant dressing nicer, but not more feminine. It would be worth it to get yourself a comfortable, well-fitted pantsuit. When higher quality and properly fitted, they can be quite comfy.