The problem is your data goes from [-6.5 8]. The 16 contour lines have been drawn for that. Then when you call caxis, you get rid of any color distinction above 2 or below -2 (>2 all have same color, <-2 all have same color). This does not affect where the actual contor lines go, though. Just the range of values used to assign colors.
Instead, specify (in increasing order) the values you want the contour lines at.