If you don't see the orange Share button in Scratch, it's because you haven't verified your email addres. To fix this, do the following.
- Go to Account Settings > Email and click to resend the confirmation email.
- Go do your email and click the link which confirms your email address.
- That should do it.
- Go to the "My Stuff" page, click on the project, and see if the Share button appears there.
If that doesn't work,
Log Out/In: Refresh the page or log out and log back in to ensure your session is active.