It’s not possible to cancel a UPI transaction after you enter your UPI PIN. If you’ve sent money to someone incorrectly, you can contact the receiver to request them to send your money back.
If that doesn't work, contact your bank for further assistance.
If your issue persists, raise a complaint with NPCI within 3 days of transaction through their Dispute Redressal Mechanism or call their toll-free number 1800-120-1740.