a play mat, no more than that

We have to play mat for our little mouse, 7 months bought, because it is crawling frantically through the house and likes to play on the floor and it really is pretty cool on the laminate. As playmat the puzzle mat is super. I thought, however, we can use it as shown in the picture build a cube or a tunnel to crawl through ... For that, however, the pieces are not appropriate, the numbers and letters fall out and so the puzzle pieces are too unstable. Next time I give rather from a bit more money and have for a better quality.