This is the best Jurassic Park homage/game I have ever seen, well done. You were able to capture the tension and genuine terror from the scene that I haven't felt since I was 4 watching it for the first time. I can't exaggerate how genuinely impressed I am with this project, especially considering you made this in a little over a month(?!).
I keep getting reminded of the Alien AI from Alien: Isolation, which is awesome. I imagine that, if you wanted to expand this, that's the approach you would want to take. Here's a great breakdown of this system:
A few minor things I noticed that could help with the immersion:
-The raindrop particle effect falls inside the car (You may have heard this a lot and if so my apologies). This can be mitigated by placing a polygon collider/trigger around the car and a script that listens for collision. Once this occurs the script would delete the appropriate raindrop particle.
-Screenshake. You have it in the car, but I think you should just have it in general. Trigger it on footsteps AND when Rexy roars (at least in close proximity).
-Rain effects on the player camera would be a simple but effective touch when you exit the car, would also make seeing the Rex more difficult (which is a good thing).
Again, I loved this demo. Can't wait to see where you go with it.