If I pick up a large pack in the discard pile and put down an incomplete 7’s canasta are there and rules or restrictions about going out without completing it?
In order to go out, you must have at least one Canasta; a complete set of 7 cards. If you do not yet have a Canasta, then you cannot go out; you must keep at least 1 card left in your hand.
A player goes out when he gets rid of the last card in his hand by discarding or melding it, provided that his side has melded at least one canasta or he completes a canasta while going out. Failing this requirement, he must keep at least one card in his hand.
You can only go out if your partnership has melded at least one canasta.
Note that there isn't such a thing as an "incomplete canasta". A canasta is simply a meld of 7 or more cards; and meld with fewer than 7 cards is just called a meld. A meld can become a canasta if more cards are added to it.