A person was praying his Ishaa prayer alone in home and as he sits in his last Tashahhud he was confused whether he missed a Rakaa. Considering it as Waswas from the Shaytan he ignored it and did Sujood Sahw after Tasleem. But when he was doing the Adhkar after the prayer the doubt came to him again so he prayed one more Rakaa after the Adhkar and did Sujood Sahw after Tasleem. Is his prayer valid or should he make up the prayer again?