Generally, you can’t rescue mugs. You want to dial in a perfect and robust recipe that will guarantee 100% success on mugs. For getting started, it is always safer to start off at 400 F for a longer time than suggested, firm pressure, and then if the first mugs are perfect, backing down the pressing time to save time, until hints of lightness occur. 400 F for four and a half minutes, firm pressure, is a great starting point to avoid any mug loss.
-Aaron Knight, Geo Knight