you can't post to Blogger using the app. There is an easy workaround:
1. Setup your Mail2Blogger posting address in settings on blogger.com
2. Since Instagram saves a copy of the modified photo in you camera
roll, just hold your finger down on the photo you wish to post to
blogger and hit "copy"
3. Paste into an email to the posting email address you setup above
That's it. The subject of the email will be the title in blogger, and
the body will remain the body of the post.