But with transubstantiation Catholics believe it is actually the body and blood of Christ, so you are re-sacrificing Him. Therefore, it can’t be a representation.
Re-presentation. Not representation. And the fact that it is Christ’s body does not mean it is a re-sacrificing of Christ.
Catholics consider Christ's sacrifice on Golgotha to extend throughout all time. It happened once in history, so it can't be a "re-sacrifice", but because Christ is eternal, so is the sacrifice. In other words, at Mass, the celebrants are in a sense present in the upper room as well as in their churches in current time. And yes, Catholics consider the bread and wine to actually be Christ's body and blood, extended and multiplied just as were the "loaves and fishes".