How to shrink 100% acrylic?

I ordered a cardigan online in the smallest size possible (small) and it's still too big on me. It's 100% acrylic. I googled if I can shrink it but I'm getting mixed results. Some say it can shrink a little on high heat and others say it will actually expand on high heat. And I'm hesitant to try it because if I wash it then I can't return it. So does anyone know how to shrink 100% acrylic??