Yeah, even if the Bible was correct, smoking weed wouldn't be a sin. Nowhere is it condemned, and probably smoking pot was completely unknown among the ancient Hebrews who wrote the thing. And it says clearly in the very first chapter of the Bible:
And God said, Behold, I have given you every herb bearing seed, which is upon the face of all the earth, and every tree, in the which is the fruit of a tree yielding seed; to you it shall be for meat.
...
And God saw every thing that he had made, and, behold, it was very good.