Bro, I am in final year and I feel the same. Because of that feeling and thinking I have left two programmes before. In total I've spent three years doing university and never gotten a degree from either university.
This time, my third attempt. I have got to final year and I may as well finish.
You will be unsuccessful if you don't make the best of the time you spent on whatever you put your mind to. In some occasions, you'll ace something in under a day, in other situations, you'll spend three days and still not get a pass mark. That is the nature of anything which tests you
For now, like someone mentioned above, just do it. Think of Nike. And be a nikey-boy for a second. Just do it. If you are focused, you'll get a good pass, and if you are unable to focus you'll miss a good pass mark. That's the end of it.
I will also second the other post about there potentially being something causing this. That's not a lie. In a time more appropriate to you (when you aren't dealing with exams and assignments) give yourself the time, space and thoughts for yourself - to figure out what's putting you off and limiting your self belief. A lot of the time, it is just in our heads. And that can be pinned down to everything that happens around us. So if you change the way you look at things, actively tell yourself to encourage yourself. You'll see steps in a direction to giving yourself more time to focus on what you intended to focus on