It's all about planning. You need to get out your calendar and work out, as exactly as possible, how many days or hours you have until the deadline. Then look at the project and try and work out how long it will take. Once you have done that, unless you are absolutely sure you know how long the work takes, add at least another 50% on to your estimate, because nearly everyone thinks they can work faster than they really can.

Make a realistic plan with generous margins to allow for difficulties, even for having to redo some of the work. Include breaks and little treats too, especially if the project is a long one. Then - start work. And once you've started, keep going. A very useful tip I learned is: If you put off a job, even a small one, you will grow to hate it and the thought of it will poison your days. Just do your planned amount of work for the day and you will feel lighter and happier about the whole thing than you could ever have believed.
Good luck!