My manager has been pushing me to move fast for the past month due to my lack of progress and as a result, I haven’t been as careful with my testing and I found a major error in my code that might set me back by a week or two. My project is essentially a data generation pipeline and there’s an error with the data generation code. I was supposed to generate data to train an ML model. I started the data generation but only realized that we had an error 1/3 of the way in.
We have a major deadline by early March and I’m afraid that there’s a real possibility that I can’t make that deadline. I have some ideas that may work (building a smaller scale version of my pipeline and train a small model to validate). In January he was worried with progress but a month later he seems more relieved with current progress, so breaking the news to him is worrying since I’d make him worry again. What’s the best course of action in this case?
As a postmortem, what could I have done to prevent this situation from happening?
Honesty is the best policy. Yes, results are important for a manager, but they're equally (maybe even more) concerned about predictability. If you know well ahead of time that something is struggling, you can react to it, either by adding more resources or creating a backup plan. Because of this, having a miss but knowing about it beforehand is easily 5x better than having a miss that comes entirely out of nowhere.
I think you have laid out your communication strategy pretty well. Communicate the following:
There is almost never anything to gain from restricting information, especially as an earlier-in-career engineer who needs a lot of support. On the other hand, restricting information often has lots to lose. In general, it's always best to overcommunicate.
On top of Alex's great answer, here's what I'd recommend going forward