Does Oxiclean Need To Be Disolved in Hot Water and Stay Hot to Work or Can You Disolve with Hot then Cool Down the Mixture

I have a linen shirt with an unknown stain (possible oatmeal or coffee). Linen will shrink in hot water so I have mixed the Oxiclean solution with cold water after it disolves.

Unfortunately, the stain hasnt come out. I am willing to risk a warmer water for my linen shirt if that makes Oxiclean more effective.