How to know when to drop a course?

I'm debating whether to drop my photography course. I'm struggling with learning the camera functions and using them effectively. I'm really better at writing/analyzing things, my other two courses are English & History courses, which I'm not really worried about. It would be good to learn but I'm afraid I'll blow it and I can't really afford the blow to my GPA. I have until tomorrow to drop it without any record of it and to get all my money back.