Can I get sued if I'm working for free to get experience?

Hi. I want to start my own event planning business soon, but I don't have any real experience other than planning my own family parties. I was thinking about offering some free event planning for a church or other similar nonprofit organization in exchange for a reference and some photos from the event. However, I was wondering if that's risky legally, could people try to sue me if they have a problem with the event even if it's not my fault? Should I have a contract even for something like what I described or only once I start my business?