Replying to When should I ask?

I want to go to homecoming with said girl. Weve been hanging out a bunch this summer. I decieded that I really like her. School starts on the 6th and Homecoming is on October 15th. I even told her I am going to ask her to homecoming. She said she knew I was going to. Now, NS, how early is too early to ask her to homecoming? I was figuring like a week after school but obviously I dont want to be too late. Cause I know Im not the only one interested in her.