the drain looks higher than the mosaic, as
@antonio has said above,
Is that right, or is it angle of photography?
Mosaic can actually be difficult to fix into a shower former if u don't know what you're doing.
If you take a tape measure, and following the contours of the former, and measure one end it will be shorter than the same measurement taken across the centre. (Through middle of drain)
With some mosaic you need to account for this variation in width, after all the mosaic are a constant size, whereas the measurements across the former are not.
This where the art of opening and closing of sheets comes into its own.