It still refers to attitude. Unworthily is an adverb and it describes the manner in which you partake of the bread, i.e., your attitude, not your own condition of sinlessness or worthyness.
A mortal sin is a sin so grievous that the sinner is no longer in a state of grace...
Where does it say that in the bible?
You're correct in your interpretation. Contextually, Paul is writing to the church at Corinth, most of whom had just recently been involved in the worship of Aphrodite. Their pagan religion involved temple prostitution, drunkenness and debauchery. At the time of the first epistle to Corinth, the church there is in major crisis, with infighting and some members slipping back into their pagan practices. Rich people were making a party out of the communion gathering, getting drunk and feasting in front of other believers who were too poor bring their own.(I Corinthians 11:19-22) Paul is telling them to be reverent about communion, and that it is a time to judge oneself. It was not about satisfying their bellies, but remembering together the body and blood of our Lord. He ends the chapter by basically telling them "No more parties, and I straighten the rest of this out personally when I get there." (vs 33-34)
Where does it say that in the bible?
Good question. Sola Scriptura
This doesn't seem relevent to the topic at hand. Isn't this thread a Catholic issue?
John 20:21-23 (KJV)
21 Then said Jesus to them again, Peace be unto you: as my Father hath sent me, even so send I you.
22 And when he had said this, he breathed on them, and saith unto them, Receive ye the Holy Ghost:
23 Whose soever sins ye remit, they are remitted unto them; and whose soever sins ye retain, they are retained.
This is how Catholics interpret the above: the power Christ gave the apostles was twofold: to forgive sins or to hold them bound, which means to retain them unforgiven. Several things follow from this. First, the apostles could not know what sins to forgive and what not to forgive unless they were first told the sins by the sinner. This implies confession. Second, their authority was not merely to proclaim that God had already forgiven sins or that he would forgive sins if there were proper repentance.
Such interpretations don’t account for the distinction between forgiving and retaining—nor do they account for the importance given to the utterance in John 20:21–23. If God has already forgiven all of a man’s sins, or will forgive them all (past and future) upon a single act of repentance, then it makes little sense to tell the apostles they have been given the power to "retain" sins, since forgiveness would be all-or-nothing and nothing could be "retained."
Furthermore, if at conversion we were forgiven all sins, past, present, and future, it would make no sense for Christ to require us to pray, "And forgive us our debts, as we also have forgiven our debtors," which he explained is required because "if you forgive men their trespasses, your heavenly Father also will forgive you; but if you do not forgive men their trespasses, neither will your Father forgive your trespasses" (Matt. 6:12–15).
If forgiveness really can be partial—not a once-for-all thing—how is one to tell which sins have been forgiven, which not, in the absence of a priestly decision? You can’t very well rely on your own gut feelings (think of the current convolutions regarding personal interpretation of what the bible has to say on homosexual behaviour). No, the biblical passages make sense only if the apostles and their successors were given a real authority.
You can read the above but with a bit more detail at "The Forgiveness of Sins"
"A mortal sin is a sin so grievous that the sinner is no longer in a state of grace...
Where does it say that in the bible?"
The relative gravity of venial and mortal sins are attested in 1 John 5:
"16 He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that you ask. 17 All iniquity is sin, but there is sin that is not mortal."
Where in the bible does it say that the the Word of God is only contained in the Bible; where in the bible is the phrase sola scriptura?
Are you a practicing Roman Catholic?