My maxima don't want to stay up right

Hi, I just bought a baby maxima clam almost 2" in lenght
I put it on my sand bed with a flat small rock underneath it
For the first couple days. It's fully open and attach to the rock under it.
Then it change position, and lay on its side. I thought it don't like the placement
so I move it to another place and it does the samethinng. I try to put it up right multiple time
but it keep lay on it side. Now it won't full open at all
I got a picture of it lay on it side and the byssal attached to the rock
Any idea what happen?
I suspect it's not happy with the placement. Maximas need a lot of light. Based on the fact you have it next to some lower light acans, I'd suggest moving it up higher in the rockwork.