So instead of blaming yourself for what happened because you suddenly need to buy another to replace it, I have a simple trick that you may want to try to grow your shrunken sweater back.
All you need is to take that shrunken garment and soak that sweater in cold water for three hours with one-half cup of plain salt (without iodine).
When that amount of time is up, gently wash your sweater as you normally do.
However, you will need to add one-half cup of a hair conditioner to the rinse water. By doing so, you will be delicately loosening those stressed and tightened fibers.
Some sweaters will return and grow back better than others. Nonetheless, this sweater trick did seem to work miracles on a few of my sweaters that I, otherwise, would have given up on as hopeless.
Just in case you find yourself in this situation, I hope you try this tip because it does help grow that sweater back!