As a pilot do you not accept being tired as a factor? I actually think my RPM control is pretty good most of the time... I just got a little sloppy on that 180.
...And the throttle-chop. But don't worry. As you say, things will get hopefully better with practice and experience. If you're up to it.
You've already learned a tough lesson: You can't be "average," ever, especially on a checkride. You have to be the absolute best you can be, 100% of the time. If you're tired, compensate for it. It's what the pro's do.
The good news is that no one will ever know you busted the checkride. When you and your instructor feel that you're ready, do it again.
And pass it next time, dammit! You know you can.