I'm sorry to hear that you accidentally put your 100% cashmere sweater in the washing machine. Cashmere is a delicate fabric and it's not recommended to wash it in a washing machine. The agitation and heat of the machine can cause the fibers to shrink, pill, and lose their shape.

If you still want to try and save your cashmere sweater, you can try the following steps:

1. As soon as you realize your mistake, take the sweater out of the washing machine and gently squeeze the excess water out.

2. Lay the sweater flat on a clean, dry towel and roll it up like a sushi roll to gently press out more water.

3. Unroll the towel and lay the sweater flat on a clean, dry surface, away from direct sunlight or heat.

4. Gently stretch the cashmere sweater back into its original shape and let it air dry.

Keep in mind that there is no guarantee that these steps will restore the cashmere sweater to its original condition, but it's worth a try. If the sweater is severely damaged, it may be best to take it to a professional dry cleaner for repair.