IMHO, I don't think it's believable for one reason... the pot.
If you put it on a slab, then someone might imagine that it's surrounded by water, or just an island of peat/soil on the Canadian Shield (or some such thing).
The only other thing that I would try, would be to try and space the trees out around the outside, so they aren't "laying down" quite so much... and, the fringe of an island of trees usually has ring of understory plants and the inside is void of most anything (I'm not sure that I explained that well enough)... even if you put a fringe of moss around the outer perimeter, but left the inside as it is, it may make a bit of a difference... but thats just me...
Personally, I think that was a steal for $100.00, I'd just look for the right flat stone around the edge of a lake... I find them all the time on the shoreline here.