Make sure you choose a mug that is large enough, so the batter does not run over.
This way, the preparation of the pancakes is made easy since all the ingredients are in another bowl.
If you see that the cake is leaning to one side, then stop heating, hold the mug again and tilt it, then from scratch start heating.
You want to make the baking time shorter in a bid to avoid over-baking, and you would always add an extra ten seconds to get the required effect.