Hello!
I just wanted to stop by to let you know that, usually, when someone says "add me" on the Oekaki board, they're referring to be added as someone who is able to color-in your drawing. You should see a little text box under your drawing that you can enter text into. Type or copy-and-paste the username of who you'd like to allow to color-in your art there, then click the Confirm/Enter/Submit button (I forget what it says) or press Enter on your keyboard.
In most cases, someone will need to be added to your art in order to complete your "Color the ___, Get a ___". This allows them to use a similar color palette, and to easily have your color-in nearby for reference.