Need some help Cuties.....

I am working on a design for my daughters 25th anniversary. This design is not a definate go... just playing around. The couple outline is an actual sketch from one of my daughters wedding pictures which I think looks great!
My problem is that in Embird I'm working on a 6 by 10 hoop and when I save the design then go out of the program and open this design again the size has changed. When saved the first time the design was 9.15 x 5.30 but when opened a second time it had changed to 9.90 x 5.72.... then a third time the size was 10.22 x 5.91, on the fourth try the size stayed as the last. Is the design going to spread to the hoop size??
..... Can anyone explain and thanks for any help!! hugs Dolly