You can use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to remove the skill points you put into Bow Expertise.
How much damage did you do to the trolls? If you didn't get very many hits in, or they did much of the damage before you joined in, maybe they don't consider it help. There is no benefit for them liking you, however, so it doesn't matter if they are angry.
