in the second sentence of the first letter, celie scratches out "i am" then writes "i have always been a good girl" why?

The novel begins with a very clear self-reassessment by the writer when she strikes out the words “I am.” Although she is still unsure of who she is now, her letters will provide a canvas on which she can openly explore this and many other subjects, painting herself into her surroundings in new ways. At this point, the opening few diary entries give a very bleak picture of Celie’s life. Still, her self-affermation that she is a "good girl" tells us that she has come to an important self-realization.