Awww, don't feel bad. You didn't mean to do it. Sometimes they move and we accidentally nick them. I remember when Hot Rod was a little guy and I was trimming his ear hair so they could stand up and he moved and I nicked his ear. He didn't react badly at all. He let out a tiny yelp but that was about it, he sat there and really didn't know what to do. I think I was more freaked out than he was. I felt (and still do) so bad! He has a little jagged mark on his ear til this day.
And then a couple of weeks ago I was trimming his backside and he moved and I got him. Well, this time he reacted and I scooped him up right away and grooming was done with. Fortunately, this time there was no blood or punctures.
I know how you feel, but just give some extra hugs and kisses and lots of lovins.