Nature doesn't curse you, kill you, maime you, smack you maybe, but not curse. Nature spirits can, but I don't see why one would be angry at you for that and a little cut is hardly a curse.
About nature smacks! My daughter was smacked by a tree this year. I told her to ask nicely before taking a leaf, she didn't, and the leaf didn't give, and when it did the branch was bent and swung at her (it was low). She wasn't hurt badly, perhaps her pride just a bit. A little red mark and she learned to respect nature more that day!
The cut may have been a reminder. You would know your guides and the personality of the spirits that work with you. Do they like to drill things into your head?
I think it would all depend on what you said in this promise. Perhaps it was a bond made through blood that was needed to seal the deal? A swap of personal possession is usually exchanged in such things. Flesh and blood is the most personal possession we have. That would be my first guess.