On first look I agreed with Suzeeq; even after I read your second post I thought that was probably right (not that Sue is wrong, the pattern is). But I went through the first decrease row and I believe your chart generator is right. That row would have to have started with 52 stitches to work it as written. Maybe it should have said CO 52 and work the ribbing. One error always makes me wonder if there are others.
If you already have the 2 1/2 inches of ribbing done I’m not sure what you should do to make it work out. That row does decrease 4X as the pattern says, but you need to start out with 52 not 50 to have it work as they say.