rueful
ROO-fuladjMeaning showing regret, often with a sad or wry smile
Memory hook a ROOF-FUL of regret. Pip kicks his new ball right onto the roof, then looks up with a sorry little half smile: “Oops.” That regretful look is rueful.
With a rueful grin, Grandpa admitted he had locked the keys in the car again.
In context Looking at the blackened cookies, Nell gave a rueful laugh: she had set the timer for twenty minutes instead of ten, and there was no one to blame but herself.
Similar regretful, sorrowful, wry, apologetic
Opposite unrepentant, carefree
From Middle English rewful: rewe (sorrow, pity) + -ful.