SOLVED. Childrens/ YA Horror novel based in a summer camp (maths?) main character has diabetes. Read around 2012-2015. [s]

[Cody]

*THIS CONTAINS SPOILERS FOR WHATEVER BOOK IT IS*
The book was based in a maths summer camp and was about this boy with diabetes. there were some spooky horror things going on but it lead to him meeting one of his old friends from when he was a child. The girls family had died on a boating trip, (I think her mum, step dad and sibling). the two of them and some other friends ended up in the catacombs under the camp, and the girl had actually lured them in there to try and kill them (I think?) because it turned out she had killed her family (she only meant to kill her step dad) and the boy fell down a ravine without any of his insulin or food. he ended up having a Hypo but they got rescued, honestly idk how.
please I am losing my mind over this stupid book I read nearly 10 years ago

[Cody]

The rockabilly werewolf from Mars wrote: "Do you remember anything about the cover?"

Maybe dark blue/ green and had a cabin on it I think, something like that. Im sure it had a really generic name, something cliche like 'cabin in the woods'

[Rainbowheart]

Do you think the book is British?

[Cody]

Rainbowheart wrote: "Do you think the book is British?"

Probably. I read it in a British high school so its probably British

[Tab]

The Trap ?

[Cody]

Tab wrote: "The Trap ?"

YES!!!!!! Thats the one thank you!!