Squeak Early, Squeak Often
The earlier you provide this information to management, the more they can do about it. Remember: Keeping management in control is in your own best interests. Squeak far enough into the project, and with enough data, and it will be clear that you’re a committed contributor who isn’t just crying wolf.
If the information you provide seems to go in one ear and out the other, start sending it by email. Daily. In most organizations, you can carbon copy (cc:) two or three levels up the chain of command in status updates; they may even thank you for it. You can also carbon copy the customer or other key stakeholders on the project.
In any event, this is a lot more than just covering your tail, although it does work wonders for that purpose. Squeaking often and consistently will lower expectations, thus formally un-dooming you.