Reluctantly
Unwillingly
adverb
If you bite into something bitter (twice!) you'll take your next bite reluctantly. Because who would want that much of something bitter? Not you.
しぶしぶ
This is the kun'yomi reading twice. You learned this reading when you learned 渋い. If you remember that, you know this too!
渋々自分がやったことを認めました。
I reluctantly admitted to the things I did.