That is not correct. You need to make sure you are doing the right thing with the units . For example you are getting:
0.34 meters x 20 meters = 6.80 meters^2
What you need to do is to do a division.
You have each ribbon is 0.34 meters/ ribbon. This makes it 1/0.34 ribbons/ meter = 2.941 ribbons/ meter
Now you multiply the two expressions together to get
20 meters x 2.941 ribbons/ meter = 58.82 ribbons
However you cannot have 0.82 of a ribbon, so you cut only 58 ribbons. They use up 58 ribbons x 0.34 meters/ ribbon = 19.72 meters
You have 20 - 19.72 = 0.28 meters remaining