It sounds like your sauce decided to throw a little temper tantrum because of the heat. We have all been there, standing over a stove and realizing our dinner now looks like a science experiment gone wrong. While the blender will definitely help hide the evidence by breaking up those clumps, keep in mind that the chemistry of the sauce has changed slightly. It might not be quite as velvety as your grandmother's version, but it will certainly be edible.
If the blender doesn't give you that perfect finish, try adding a little more fat—perhaps a knob of butter or a splash of fresh cream—while the sauce is warm but not boiling. It acts like a peace treaty for the proteins. Just remember that next time, the cream needs a slow introduction to the heat, much like a first date. No need to rush into a boil right away!