There is no pre-defined right or wrong answer. As always, what matters is your thinking process.
Here is what you need to do in these situations:
1) Assess the situation. Is this a critical mistake impacting the recommendation or a "must-have" analysis?
2) Be aligned with the firm's core values. Bain values being "true north". If there is a mistake impacting the recomendation, you have to "come clean". (if it does not impact the recommendation, you still have to make sure the client gets the corrected analysis).
3) Bring a solution and not just a problem. For example, you will make sure the whole document is reviewed again for issues. You want this to be a one-off problem. For example, you will evaluate the alternatives of doing a different (and quicker) analysis, or the possibility of doing a preliminary analysis (taking e.g. 2 days) before the full 1 week analysis, or reassign someone from a different (less critical analysis) so they can give a hand at the other task and get it done within the alloted time frame.
4) Demonstrate they can trust you to be alone with the client. Clients will many times try to convince ("junior") consultants to do certain analysis. We expect consultants to direct the clients to negotiate with the managers (and if the analysis is out of scope, they will not decide before taking to partners). In other words, you always have to align your suggested course of action with the appropriate authority in your team. This part is critical. While postponing the steering committee is at times acceptable, doing so without consulting with the partner first would be a huge mistake, as they could feel you were mismanaging the client.