I agree with the other post. That looks like a normal glue line.
When I do my final sanding, I round over the edges of the bamboo to have a smooth transition and reduce the possibility of fibers lifting, and that normally reduces the visibility of the glue line.
It's not related to your question, but it looks like your bamboo is a little thicker than 1/8" an inch. It may not affect this bow, but I would consider it on your next bow. Especially if you intend to use a stronger belly wood in the future. The tips of your belly wood will be very thin with 1/4" of bamboo.