On The Contrary, Instead
adverb
Something that is contrary... this is the te-form version of contrary, meaning you're starting to say something, making this on the contrary.
かえって
The reading is like 変える, which is to change. So, if you change what the other person is saying to another way, then you're saying you're changing things. It has the same reading, so remember it that way.
善かれと思ってしたことが、却って仇となって友人のストレスになってしまいました。
I just wanted to do the right thing but instead it backfired and I just stressed my friend out.