Im scared to ask someone to go to the dance with me?

i have a dance this month at my school and there's this boy in my homeroom cl who i have a crush on so i was thinking about asking him to go to the dance with him i asked my cousin which she goes to my same school she also has a crush on the same boy but she's going to the dance with her bf .she told me ask him .Im scared because what if he says no .i know that usually guys ask the girls to go to the dance with them .Im to scared to say it in person so i was thinking about writing him a note i think all i should write is will u go 2 the dance with me i have a group project with him so that will be a easy way .please help me !!