From the Han trainer online, for the separate characters I get the following:
对 (dùi) = correct, versus, facing, for, to oppose, pair, as regards of, right 不 (bù) = not, no, negative 起 (qĭ) = to raise, to rise, from, start, to establish, to appear, to get up, to set up, beginning
And while you should probably be careful in attributing meaning to character combinations simply based on the meaning of all the separate characters, it can be helpful sometimes. Like here, with a little imagination you could use this as a mnemonic for something like "Ow, don't start (to thank me)"
I found this to be a useful breakdown https://www.thoughtco.com/dui-bu-qi-saying-sorry-2278549
It's very frustrating that duolingo doesn't give you the pinyin alongside the English when you click on the characters for help. You only see the pinyin once at the start of a lesson and then you have to guess based off the audio in future questions. Not useful for learning in my opinion.
Posted in a reply but this link is a useful breakdown of meaning by character - https://www.thoughtco.com/dui-bu-qi-saying-sorry-2278549