Working on E4 Scope is not going as planned

First off, don't panic - It's not expected for an E3 to perfectly deliver on a project that's above their level in terms of scope unless they are a more "mature" E3 (1+ YOE at the company). My main advice is to have stellar communication around the delays. Explain what they are, why they're happening, and what's your plan to address them. Here's a similar thread, also from a Meta engineer: "Got hit with a last minute requirement on my project - How do I minimize the thrashy impact it has?"

If the deadline is slipping real bad (1+ week), you should figure out how to make things go faster be talking with your tech lead/EM/PM. There's many possible avenues here:

1. Cut scope
2. Bring in a helper
3. Allocate more of your time to the project
4. General workflow improvements (add or remove meetings)