how to ise spet blend with sketched section?

hello guys i'm trying to build this part which has a variable protrusion so i'm trying to get than through swept blend with sketched entity
now when i select the orgin ro curve which is supposed guide my sketch
and it is lying on a base feature but it is not normal to base feature which is creating a gap
for better i'm attached three picture
1) drawing of the sketch
2) ok part from the book
3) my problem
please go through you will understand