No. It is not a rash or sunburn that will remain forever and leave a mark on your skin. Sex Flush will go away in time. When you sit under a fan, apply cold water and ice on the portion of the skin where you experienced sex flush and taking sufficient rest will ensure disappearance of sex flush.
For some sex flush may take upto 2 hours to disappear. There is nothing to worry about. This is absolutely normal. The duration may wary from person to person, though. For some, it may take a little while than others. But it will go off completely and there is no need to worry about it.