The black fabric you are trying to use is not a good match for your patch! It looks like lingerie fabric, or some such thin material. I would not use that, even if it is the right color!
(You can test for cotton fabric by usig a match and burning a thread. Non natural fiber melts. Natural fabrics will burn.) Mixing fabric in a quilt is usually not recommended. Crazy quilts are an exception. Anything goes, but they are usually not expposed to heavy wear, nor laundered.
BTW, trim the seams where your corners overlap. You will be happier with the end result.
Go for the fun, but remember we have most likely made these mistakes which is why we are giving this advice. :?