I use Epiduo as well. For me it's impossible to use only a pea-sized amount on my whole face. Use like 3 peas in total. One pea on my left cheek, one pea on my right cheek and one pea on my chin.

But the general rule is a thin layer on your affected areas.

The standard application for epiduo should be two peas. One pea for T-zone (forehead, nose all the way to chin) and the second pea to all other face area (cheeks). I use epiduo gel that contains 0.1 % adapalene and 2.5% benzyol peroxide.

They say a pea sized to the affected area. Well everyone doesnt have the same amount of breakouts so just use enough for a light layer over all the affected areas.

I would say a thin layer on the area. Or a pea size. Also i find topicals work best when the skincare is kept very simple-

Ive been applying a pea sized amount to each affected area for a week. Is it too late to change to a thin layer or can i still do it with no problems?

Just make sure you're using a thin layer on the areas prone to acne.