Min the calage is great. I love the way you have used your colors, but I have to agree with the teacher. I was always told, that when doing a mount, that I used one of the colors in the creation. I was told that it give it a much better contrast to it, and as Sandro mentioned, and I have so many times when mounting a photograph, used double sided tape. It will stick solidly the mounting, and if you have to remove it, there is no tearing of paper.
I agree with Sandro, let us see it when you have completed it. I say,
GO FER IT!!!