The hard conversation with your manager is part of the job. Avoiding it doesn’t shrink the problem.

Problems rarely deflate while you avoid raising them; they get more expensive, and your part gets harder to explain. The dread is mostly about the first thirty seconds, which is a small price next to carrying the thing for three weeks. Managers generally prefer the version where they hear it early. Saying the awkward thing is a skill that gets easier with use rather than with waiting.

Write the first two sentences of what you need to say and keep them short. Find a quiet moment at the start of a shift rather than the busy middle. Say it, then ask what they would like you to do.