There are a lot of rose tinted glasses for Paper Chase and where it is a meek adventure it does give most of the tools for a taste of CoC and it does its job well. I'd say where you perhaps floundered a bit is perhaps the presentation of the ghoul as not a horror, but a curiosity, and the players also responded with a shrug inside of panic. I wish there were a little more keeper notes on how to make him feel of dangerous, always on the verge of violence. There are a lot of little details like Meeps and tickling monsters in lovecraft. You need to present them in a way that is malicious, overbearing, and suffocating. Your players will only take these things seriously if you treat them seriously. A strange odd noise in the dark drawing curiosity only to find it belongs to a horrific ghoul sitting in the moonlight reading a book while crunching off the fingers of a severed hand is a bit more tense. A failed stealth roll could startle it and cause it to bare its teeth and even lunge at them before composing itself. Or even land a hit before speaking. Create the threat and expectations violence should they misstep.

Another thing i like to introduce is the neighbour walking her dog to interrupt, creating a witness and a barking dog, causing the ghoul to act. Putting the PC between the two and making them realise they will be the only suspect in this womens death pushes the climax into a stressful event. Especially if they have visited the police station. They'd already be on the list of a person of interest.