Either you have forgotten the sun protection milk or you did not apply apply all over or suddenly the shadow was gone or you simply ran out of luck. And now the skin is reddened and burns like hell.
But there is an easy method: simply lay the SilverButler (the silver cloth, which you should have always and everywhere with you, because it fits in every, even the smallest pocket) on the affected area. Silver cools very efficiently. Dampen the cloth enhances the effect by evaporative cooling (if no water at hand…the own spit does the job too); the heat is quickly transported off the body, burning is stopped; noticeable relief comes up.
Repeat this process (wettening the cloth, laying 10 minutes onto the affected area) several times. After the second time, you may experience the burning becoming less. Often the burn is „transported off“ after an hour and you might feel well again.