I didn't want to leave a negative comment in the forum as it's such a small thing and the rest of the clip is truly amazing, but the only note I have is that if you'd been able to film the actress against a glass wall, then her hands would have stayed still, as them moving about as she holds them in the air is slightly distracting.
I'd also did not expect a slow fade on the last two tiles over her face, as the previous tiles had appeared singly and faded in quite quickly, so until then they seemed to be shutting her in in more solid way, not fading into place. The last tile appearing quickly with a musical cue might have been more final, so tile, tile tile, tile tile......<music rises> Last Tile!
But, truly impressive in every way, story, FX, pacing, good use of not showing too much without falling into the traps of hiding things behind the camera or out of shot. Also us seeing the corridor had grown in both directions just before she turned her head to see it created a great feeling of anticipation for her turning and seeing it.
Very, very impressive and it skillfully sidestepped all the usual "What's going to happen now? Will it be a jump scare or just something horrible to look at? <Yawn>" that some lazy "horror" films fall into, and was genuinely creepy.