I’ve got to get this project finished until tomorrow.
Correction: It should be by tomorrow.
You use ‘until’ to mean ‘up to a particular time’: We’re here until tomorrow. I’ll be working here until Friday. We have until 3pm to get the job finished. Until is used to talk about the period before the deadline.
By is a time preposition and tells you when the job or activity is to be complete. It means ‘on’ or ‘before’. It tells you when: We’ll here but we should be finished by Friday. We’ve got to get this job finished by 3pm or we could be in trouble.
To summarise, ‘by’ is used to focus on the deadline and not before it, while ‘until’ focuses on the period before the deadline and not on it.