YouTuber @mogutty told me they had some artwork stolen from an exhibition when they were 12. Since they that have not used a sketchbook in case they lose it.
I think that they were probably told a story when they were 12 and have let that ruin their lives ever since.
Firstly make sure your name and address and email is in the book so people can send it back to you. Moleskines have this printed on the inside cover and suggest a reward for finding and returning. Most people will understand how precious it is to you and return it anyway, if they can.
Secondly, try a smaller book, with fewer pages. Then if you lose it you haven’t lost too much.
Either way, a sketchbook is for fun, for reference. Don’t take it too seriously, it’s not a michaelangelo, it’s the preparatory work for your masterpiece.
Don’t create excuses that stop you getting on with the real work of learning how to draw. You can only do that by drawing and a sketchbook is a great place to do all that practice in.