I’m glad to hear you appreciate you could have done better. I set high standards, and I respect those who set the highest expectations for themselves.
Clearly, the most appropriate consequence of a disappointing grade would be A Note From School.
Write a note, perhaps describing where you fell short and how you could do better. Make it constructive, practical advice. Then you can put it in a sealed envelope and carry it about with you. A continuing reminder of your aspirations to do better.
And, of course, any student bringing home a note from school might very well expect a spanked bottom when they get home. Several spankings even. But I’m sure you’ll use your cornertime constructively, vowing to improve as you stand there with your pink cheeks on display…