Rotten squash question

Last year I started a garden for the first time. Learned a lot! When I picked my squash last year it seemed fine, then I kept it on my counter for maybe a week before I noticed a small rotten spot on the underside. Eventually the rotten spot grew and I just composted the whole squash.

Not sure what went wrong. Was thinking -should I put hay or something under my squash when it starts to grow on the dirt?