Yes, I believe one can become too scrupulous. I have done so in the past and it did not help me one bit. In fact, it hindered me spiritually. I don’t think it is a mortal sin, but my scrupulosity was nearly an obsession and along with it I often did not forgive myself following Confession and Absolution, and that is considered a sin. I have prayed profusely and asked Our Lord to help me with this and He has. My scrupulosity once kept me from happiness and joy. Now, with the help of several priests and Jesus this affliction has been lifted. Thank God!