| | Re: There are gaps in my woven headbands...
I think the teeth are your main problem. I'm new to making woven HBs too, and didn't have the money to order the flat ones from a wholesaler, so I picked up some from then Dollar Tree. They come with a colored sleeve over them. You just cut that off, and presto, you have a blank flat headband!
Tension is very important. I use an alligator clip to keep the weave in place. Every inch or two I move it up so if my hands loosen, my work won't. If you have issues with it loosening on you frequently, you could also use two clips. Just like moving score pegs in the game Cribbage, you move the the back one to the front, so the one that was in front keeps your previous place.
If you are using a wider ribbon, I can see how gaps would be more visible. I only use 3/8" on mine, so if there are minor spaces, they don't show up as much.