I usually say subhanrabbiyal adheem once in prayer. While doing this i by mistake didn’t finish it and continued saying it while standing up from ruku, a part of it. I did say Allahu akbar after. So my question is, is this rakah valid? What do i if not? Pray it again? Sujud as sahw?

Ustadh AbdulAziz al-Haqqan

Well this teaches u a lesson to say it 3 times akhi so that u don't fall into waswas.