Switching from regular SIM to nano SIM

I just bought an iPhone 5c, for which I will need a nano SIM, but I only have a regular SIM card. I know, in theory, you can just cut the SIM card to fit the nano size, but I'm kind of scared I would mess that up. But I also don't want to buy a new nano SIM card because I want to keep my number. What do I do?