I don't know about your bow but I'll take your camera. That's a great picture!
But seriously, I tried string, and it can work but wire is easier and works better for me. As for the bow you made, I think it's a great start and I would actually make a couple more loops (because it looks like you are using a narrower ribbon)and then it should look pretty uniform. That might be why it's parting in the middle. Starching it or using a stiffening spray also helps alot to make it set where it's supposed to. I also like to use different widths of ribbon, especially a wider one. If your loops get a little floppy, you may be making them a little long, so just pull them in.
These are fun bows to make and I think you did a great job, especially for your first! Keep it up. Hope this helps a little.