Three things really helped me get it to the finish line:
1) I listed out all the possible features of the project, then marked only the features I absolutely couldn't launch without as MVP. I used https://workflowy.com/ to do this because I liked the hierarchical structure and the ability to cross off features as I implemented them. Whenever I worked on my project I'd have workflowy open in one of the browser tabs.
2) If I didn't feel like working on the project I'd open up the feature list, pick one of the simplest items, and implement it. I found that if I started writing even just a few lines of code it was enough to motivate me to keep at it for hours. This was especially helpful as I got closer and closer to the finish line.
3) As others have mentioned here, launch your project as early as you can, even when you still feel "embarrassed" by it, and tell people about it! Looking on Google Analytics and seeing even just a handful of people using my site was incredibly motivating! It made me want to continue improving the site just so that those few people would have a better experience.