that liner should be sloped towards drain. Can't really tell from pictures but doesn't look like it is. Liner covered by cement board is fine but penetrations with screws is bad. On top of liner it should be mortar bed. It is not poured but packed. Surface of that mortar bed should be sloped as well. Not sure how you poured concrete to create such slope. If I were you and this is current state I would just cut liner out, tear out drain. Install kerdi preformed shower base and drain, add kerdi bench of any kind, complete everything with kerdi membranes and bands. It is much better system just because there are less material that gets wet.