Is my book any good I want to know please?

I like the idea, but some of the details should be changed if you can live with doing it. First of all, I'd make the scar on his arm or shoulder rather than head (like Harry Potter's) I'd also change the name from Percy to Peter or something as the Percy Jackson series (which features monsters as well) is very popular. I get sick of my work being compared to the more "popular series'" but in the writing world we must pay attention to things like that unfortunately! I wish you sincere good luck in writing your story!