If You truly understand how both biblical statements: that Christ died once for sins, and that -at the same time- He was the Lamb slain from the foundation of the world, are simultaneously correct, then why do You persist in Your conviction that Mass or Liturgy sacrifice Christ "again"? :-|I answer:
a) As I pointed out at this link, the term "from the foundation of the world" is best understood as modifying "written" not "slain."
b) As also pointed out there, if the term were to be referred to "slain" we would simply understand that as being a figurative expression as to the intent and purpose of the lamb from all eternity, namely to be slain.
c) One of our complaints about the Roman masses is that they don't claim to represent the sacrifice of Christ, but actually to involve the sacrificing of Christ. The Lord's Supper does illustrate for us the death of Christ: it is the true icon of his body and blood, which was shed for many for the remission of sins. The historical event of the cross, however, is complete. It is finished. It cannot be repeated or continued.