i've never made an entire jane so i have no clue how much fabric you really need.
i'm going by what the software says which is always over estimated. every EQ project i've done always has more than enough fabric estimated.
if you're going for a scrappy look i think its ok to just buy as you need because nothings supposed to match any way.
if you're not doing a scrappy and pulling from your stash i'd be a bit more careful and double check online that you can still buy some of that fabric, if need be.