Pretty cool! You can definitely get a better sound easily, though: it's all a bit too dull for a horror track in my opinion, the large reverb is engulfing everything. Everyone is like sitting piled up on one another at the back of the stage. You'll get better horror by bringing forward and really in-your-face parts of the orchestra. The dissonant violins for example can have a really nice stressful effect if they sound like they are just behind your ear...
The heartbeat at the end sure sounds nice, and who doesn't like a heartbeat sound in a horror track ?
but I don't think we hear it before at all, so it's kind of coming completely out of nowhere.
Don't be afraid of using silence! Well, you should be afraid of silence
but use it! In a horror track silence is the most important instrument of all! Just watch and listen to the film Ring (1998, the original Japanese one). Or Dead Space for that matter. In the soundtrack nothing ever happens. And then BOOM! violins playing horrible clusters fortissimo! Obvious, but still gets everyone every time.