I expect the unexplained difference in the ending capital balance is caused by distributions out of the partnership to you. Those distributions typically are subtracted from the beginning capital balance - along with your attributable gain or loss - in determining the ending balance number. A negative ending capital balance figure is treated in effect as a capital gain.
I wholeheartedly agree with @Anonymous that you take all your paperwork - prior year income tax returns and those Schedule K-1s - to a local pro who has some experience with these things.
