It's your life, so don't think I am telling you how to do it but...
Garbage in... Garbage out. If you use good quality stuff, your finished product will be nice.
Life is too short to use crap. Even free crap. What you are trying to accomplish is just about the easiest thing to do in quiltmaking. If it isn't working it isn't your fault, it's the fabric. Get different fabric. A yard of Kona black cost about $6.00 even out here in expensive California, less on sale. If you are not willing to invest $6.00 into your craft, well...
You have your answer.
tim in san jose