Gomenasai, I know i let you down.

对不起，我让你失望了。

youdao

I know I let you down, didn't I?

我知道我让你失望了，不是吗？

youdao

I've let you down, I know. All I can do is to promise to try and do better.

我知道我辜负了你。我所能做的只能是保证努力做得更好。

youdao

"I know many have been so supportive during this campaign and I hope I have not let you down, " he wrote.

BBC: Lee Baron, Labour

You know, I've been discriminated against, but I'm not going to let it hold me down.

NPR: Robert Glasper: The Inauguration Session