The short answer
Business contracts generally have no cooling-off period. A signed contract can be undone only on limited grounds, such as lack of capacity, duress, or certain mistakes. A court can also correct a document that does not reflect what the parties actually agreed.
Where it fits in your case
Shortly after signing, or when the other side seeks to enforce terms you believe are not the real deal.
What to expect
Capacity. Severe intoxication or illness can matter if a party could not understand the transaction.
Duress requires a wrongful threat that left no reasonable alternative.
Mutual mistake about a basic fact can allow rescission; one party’s pricing error usually does not, unless the other side knew or should have known.
Reformation fixes a writing that misstates an agreement, usually on clear and convincing evidence.
What we need from you
Drafts, negotiation emails, and the circumstances of signing.
Common misconceptions
“We have three days to cancel.” That generally applies to certain consumer deals, not business contracts.
“A bad deal can be undone.” Regret is not a legal ground.