Trying to use Sun-In? not working?

so i keep putting a load of this sun-in in my long brown hair. its not dark brown, its rather light but its definitely not blond. i used sun-in once and i sprayed like half of the friggin bottle in my hair and it barely did anything. so then today i used a lottt more and my hair looks the slightest bit lighter. am i missing something here? because my 3 friends did it and they're all pretty much blond now.