Disgrace that, job the new build I've just done was had mastic all the way round exactly the same. I cut it all out before I even screeded it. Silicone around Amtico/Karndean is a big no-no for me, all i do is put it tiny slither around the base of toilets to stop drips from missing the pot. I'd complain and say you want it fitting correctly.
This is how it should fit https://www.instagram.com/p/BnpOJFunMM_/?utm_source=ig_web_button_share_sheet
I should hope you did! I have seen new builds been screeded without removing the gunk before, shocking