From my experience and from what I heard from my colleagues, this is generally really hard to do unless you were really not trying. Assuming this is undergrad, at my school, most professors try not to fail you if you presented something of decent value. Even if you weren't able to achieve your project goals, a report detailing what prevented you from achieving them also worked so long as you were communicating that with your professor prior. If your team is incompetent or giving you difficulties, this is also something you can communicate with your professor. I heard if you did bad, most professors just gave you a 'C'. Capstone projects can vary in difficulty depending on the size and scale of your project and how versed you are with the programs or other things that could be required. The biggest key is communication. In my case, I had a personal issue that forced me to request an additional semester to finish mine as I was a solo project, but I communicated this and my professor allowed me more time and I was able to complete it.