No need to toss your fabric, but from what you have said, it would appear that you are using the wrong product.
Retayne is what you need, to set the dyes .............
My understanding is that Synthrapol will not set dyes, to keep them from bleeding.
What it does is to pull out the dyes, and keep them from staining your fabric.
If there is excess dye, then it will keep coming out .... as that is Synthrapol's job.
Just follow the instructions on the Retayne bottle for use .... and for laundering your quilt afterwards too.
I keep Retayne on hand, and any questionable fabrics, get the Retayne treatment!
Good Luck!!