I signed a lease but haven't moved in yet. Don't I have 3 days to cancel the lease?

Contrary to popular belief, Texas does not have a "buyer's remorse" law for leases, according to the Austin Tenants' Council:

Myth: A tenant has three days after signing a lease to cancel it without penalty sometimes called “buyer’s remorse.”
Truth: Texas has no “buyer’s remorse” law for leases. A lease becomes binding as soon as it is signed.

They address many other commonly held beliefs on their website, The Myths of Renting in Texas.