Have you got a map? You have plenty of time to make it to Sao Paulo by any of various routes. No one here can speak to "backtracking" unless you tell us which way you've already been. What's more, it'll be difficult to suggest a route unless you say something about what sort of riding you like to do.
In particular: do you like red mud? Or would you rather stick to pavement? If the latter, you're not going to want to head south from Manaus.
Fill in the details, then sit back and wait for replies.