It should be yn, but because chi ends with a vowel, you take away the y and put in the ' to show there is a letter missing.
I believe it's a shortened form of 'yn'. (Don't quote me on any of this) I think it's dych chi yn hoffi, but they abbreviate the chi and yn to chi'n.
I didn't. Sometimes I completely miss the r though, I think it's one of those things that is said super fast and runs into the other words. Sometimes I listen to the slow mode. That helps.