Your face is not flipped when you take a selfie. The preview is flipped to make it easier to use, but the image captured is not on any phone I've seen. Both the front and rear facing cameras work just like normal cameras. If someone was looking at you taking the photo and held it up in front of you, what they see in the photo would match what they see in real life.

If you want to flip it for some reason, you are welcome to do so. There isn't any rule against reversing an image and it is sometimes done for different artistic reasons, but it's entirely your call.

If you are just worried about it being backwards because you had the display facing you when the camera was facing you. That simply isn't how it works, so you don't have to worry about accounting for it.