Shine a light into the darkness.
If the last 10% of the project takes another 90% of the time, that’s bad.
If weeks go by without visible progress, that’s bad.
What you need is a lot more openness. A lot more transparency. People should be able to see, at a glance, the current status easily.
Unit tests provide evidence of robustness, correctness, low coupling, high cohesion. If you’re practicing Test Driven Development, you will have lots of unit tests. Your test suite will be able to tell the story.
Kanban shows work in progress. There is nothing like having a highly visible Kanban board to constantly remind people what the current status of the project is.
Incremental development increases the visibility of progress by increasing the frequency of development evidence. The more frequently you deliver, the more often the business can stand up and take notice. Working software is real evidence of forward progress, and it increases trust.