there are many different paper backed fusables on the market- you want to make sure you use a (lite) one- such as steam a seam lite- or heat & bond lite; wonder under is another-
the heavier fusables do not soften up- they are better suited to use for wall hangings or purses/totes-
if it was easy to sew through you probably have the right one- and it will soften up-
but if it was difficult to sew through- or gummed up your needle at all it is probably one that will not soften up.
it is important to read the packaging-instruction sheet that comes with any fusable to make sure you are getting one that is (correct) for your use.
you will have to finish-quilt and bind the quilt- then wash and dry it to find out if it will soften up -
good luck