Illustrator: Fill shape made of lines?


Hi, I'm very new to Illustrator and am using online tutorials to help me. I have made this shape using individual lines, however all I want to do is fill the centre of it, but I cannot for the life of me work out how to do it. I have tried the paint tool and fill. As you can see I have expanded it to make into outlined paths (sorry my vocabulary is very basic). Please may someone advise on how I might be able to fill this shape I have made, or advise a better way to design this if I shouldn't have made this via individual lines!
