next time you need to purchase binding fabric- first find how long of a binding you need- (your current project of 41x61=)
41+41+61+61= 204", I generally add about 10" for joining ends & mitering corners- so now you are at 214" needed
divide that total by 40" (figuring cutting off the salvages- that's an average length) you need 5 1/2 strips (figure 6)
6 strips x your 2 1/2" width comes to 15" (so, a 1/2 yard would have been enough)
any other size- figure it the same way- the two measurements x 2 (for all 4 sides to bind) plus excess for joins, corners- figure the number of strips needed-based on the usable width of the fabric- then multiply the number of strips by the width of the strips to see how many inches of fabric you need.
I have found most Joanne's employees know very little about the products the store sells- are seldom sewer's or crafters- most of them at our local are college students who needed a 'retail' job. any retail would work.