Usually when someone is getting watched or stalked, there is this some kind of 6th sense where the person that is getting watched would feel being watched. You could more like build up the panic and uncertainty of the player and make them have an urge to turn around more frequently (or if completely scared, not turning around at all) and to hint out someone is watching them, you could maybe write some text about the player feeling not safe at all.
ill probably add the eye back and some ambient music, Thanks! Getting the player to feel that 6th sense on a video game is quite difficult but ill try and pull it off.
You could also try playing small sounds that dont necessarily obviously give away that someone is watching, but can be perceived as someone watching.
To be more clear, the ambiguity of the sound’s source and what the sound is can make the player feel like something might be watching but not know that something is watching.
For example, a quiet creak sound could be played behind the player, this could just be sounds of the floor settling but it could also be something alive back there.
A game that does this well is Phasmophobia, there are occasional creaks and tapping or sounds similar to footsteps, that dont always directly mean you’re with the ghost, but can make the player feel like it is watching them.
As someone else said, small sounds or changes in the environment that can be subconsciously picked up by the player are a good way to do this. I also have another idea, though it is hardly as subtle as the first. There is an enemy in a game called Voices of the Void that watches the player and very slowly turns their camera to face towards it when they stand still. This builds a lot of tension for when the enemy actually attacks, far later. (If you want to know more just search up “Voices of the Void sleep demon”)