1.) Remix 2.) Add a little bit to the line (not just a straight line) 3.) Invite someone to remix yours 4.) Add it to the line 5.) Repeat the process YOU CAN ONLY REMIX THIS ONCE.
When I said to add a little bit to the line I meant that you have to make something out of the line. As an example you could make a hill or a circle on top of the line. You don't have to just make a straight line.