The traps do isometrically contract during a barbell curl. I would personally just take some time off and come back and then have your form checked on the site. There's no way you can check for every angle of your body to assure good form by just looking in a mirror; that's why videos are important.
I had a client one time pull his lower back before he hired me to train him. He was doing what he didn't know was cheat curls and got significant pains in his lower back and eventually rehabilitated and got on the right track.