I have read a lot about copywrite and my brother in law has had bad experiences with copywrites. Someone stole his design and they ended in court and they both have huge court fees and neither one won. The other party gets to continue making my brother in laws product. It doesn't stop someone from taking your design and making their own thing with your design.
I sell patterns on ebay and I'm not going to get a copywrite for them. I do put the copywrite symbol on showing that I am the author of it and it should not be copied but it won't stop them if they want to steal it. I'm not wasting my time and money into copywriting since it doesn't protect my interest like it should.
The choice is yours but unless you are going big I wouldn't bother. Good luck in what ever you decide. I like the other girls idea about having a friend try out your pattern, it is a great idea. Bernadette