School, Magic pencil that when use can change the future

Hello it’s me again and this time for a book I remember not one from my friend now I was very young when I read this book in class so I may not be remembering it right or it might not be real at all I only believe this because of one scene I remember I’ll get into that in the information part

Information
The book I remember was about a person or a group of people who discover a magic pencil and whatever they write with the pencil becomes true

The plot I don’t remember much but I remember a couple of main details firstly being I believe one of them wrote that they would win the lottery and another person wrote (this is the part I’m not sure was real) That someone would get their throat cut and if I remember correctly it happens by either the giant lottery check or a big piece of paper I believe that is when we stopped reading the book as well maybe because of that but I do believe that he survived

Sorry I don’t have more information this is all I could remember and again I read this when I was young and I do find it hard to believe that they would read us a book with someone’s gets their throat cut

So again sorry I only have so little information to work on but I hope it helps

I have never read the book myself, only saw the movie adaptation - which is supposed to be only very loosely based on the original book. So it's a long shot, but 'magic pencil and what they write and draw becomes real' and it all spiralling into the dark side sounds a bit like
Marianne dreams by Catherine Storr. ...