Why did Tom Sawyer wish he had a clean Sunday school record?

Tom wishes he had a clean Sunday-school record, so he could die..... temporarily.

If he only had a clean Sunday-school record he could be willing to go, and be done with it all. Now as to this girl. What had he done? Nothing. He had meant the best in the world, and been treated like a dog—like a very dog. She would be sorry some day—maybe when it was too late. Ah, if he could only die temporarily!