I have noticed (for some time now) that quite a few of the patterns have some errors in them that will keep others from being able to do them. Such are the little beds. There is a difference in the sizes of the beds and that is because the bedspread is what determines the width of the bed quite often. Sometimes it is the headboard. The idea to help you with this is to try either the headboard or the bedspread whichever one looks more intricate in pattern and my be the determining factor in the size of the bed.
Also if the size of the bedspread is too large then try a finer thread (like size 20 if the pattern called for size 10 thread). A nice width for a Barbie size bed is 7 inches wide so you can have a guideline to go by.