Help! I need some advice about something very stupid that I did...?

Call your co-worker immediately and apologize for taking the money. Explain the situation and she will more than likely understand. Make sure to take a breath and relax, you are going to need to calm down before you can go ahead and face this problem, and if you need to explain the situation do so. About the cameras. . . they probably check them on a constant basis since you work at a jeweler, just brace yourself for the consequences.