Are you saying that choosing and avatar (or not) and inviting people from LI & Twitter (or not) has to be done to sign up? If so, remove those steps. Signup should be as fast and easy as possible. Get people using the meat of the app ASAP, and worry about silly stuff like avatars later.

I'd ditch the LI/Twitter invite stuff, too, if it's supposed to be for "team members". Team members use email to communicate, not LI/Twitter/FB/Social Media.

EDIT: From your website, I can't tell what your app actually does, and why I should use it. I suspect people who install it don't know those things either, and that's why they abandon it.