Hey,
I don't really have a specific programme for my covers. I literally only properly made one for my second fic and I just edited over the picture in Paint...
Sorry I'm not much help :S
It's fine. I thought you used the app like I do, but I use PiCollage but it doesn't properly fit the cover onto the cover picture thingy and I can't use the Wattpad Covers app because I can't remember my password.