Lots of stuff in the Bible is contradictory, Kayleen. Fanatics will loudly use the verses that they agree with, and then quietly ignore the contradictory ones.
Yes, the Bible does say this:
" ... do not have sexual relations with your sister... " Leviticus 18:9
But the Bible also says a bunch of other stuff that is totally insane:
"... a woman who isn't a virgin on her wedding day shall be stoned to death..." Deuteronomy 22:20-21
"... whomever blasphemes the name of the LORD shall be put to death; the whole congregation shall stone the blasphemer... " Leviticus 24:16
"... if a man commits adultery with another man's wife; with the wife of his neighbor, then both the adulterer and the adulteress must be put to death... " Leviticus 20:10
"... you shall not allow a woman to live who practices sorcery... " Exodus 22:18
"... anyone who dishonors father or mother must be put to death for they are guilty of a capital offense... " Leviticus 20:9
"... you have six days each week for your ordinary work, but the seventh day must be a Sabbath day of complete rest; anyone who works on the Sabbath day must be put to death... " Exodus 35:2
"... your male and female slaves shall come from the nations around you; from them you may buy slaves... " Leviticus 25:44
"... a woman should learn in quietness and full submission; do not permit a woman to teach or to have authority over a man; she must be silent... " 1 Timothy 2:11-12
"... if a man lies with a male as with a woman, both of them have committed an abomination; they shall be put to death... " Leviticus 20:13
"... if a priest's daughter defiles herself by becoming a prostitute, she also defiles her father's holiness, then she must be burned to death... " Leviticus 21:9
"... do not trim off the hair on your temples or trim your beards.... " Leviticus 19:27
"... if you hear that in one of your cities... that certain worthless fellows are saying, ‘Let us go and serve other gods’... then you shall surely put the inhabitants of that city to death, devoting it to destruction, all who are in it and all of their animals, with the edge of the sword.... " Deuteronomy 13:12-15
Question: If even God manages to get His Word so screwed up, how in the hell does He expect us to make total sense out of it???
Answer: It's pretty much impossible.