Shouldn't the finishing stitch/quilting on the back of my quilt, look nice like the front? On the back it's doesn't look nice,there is somewhat a loop on the stitches on the back. When I do a straight stitch there 's no problem. What am I doing wrong?

You are talking about the quilting? You may need to adjust the tension on the machine because of the thickness of the quilt. It's always a good idea to make a little test sandwich and practice on that until you get the tension right. In this case, if there are loops of top thread on the back, it sounds as if the top tension needs to be tightened (turned to a higher number). You need to adjust the tension until the back looks just the same as the top.

Were you free motion quilting? Stitching in the ditch? Using a walking foot?

It does sound like tension. If you have loops on the bottom, check to see if your top tension is tight enough. Sometimes they loosen up with the vibration from your machine. Tension can never tighten itself although it can get hung up on something and make it appear to be too tight. If it is too tight, sometimes it can slip out of the tension disk which will result in a loopy bottom.

if the 'eyelashes' are just on the curves, try slowing down on those curves.