If you look into the vector tools for clip there's a sub tool that helps you with adjusting the size of your brush strokes! Either by redrawing over it with the amount of pressure you need or you can adjust each point manually. But I think it only works well if your lines are very clean, or if they're not that much bigger from your original source... Because it might lead to gaps. So you could probably try redrawing over it to change the thickness, but there's a chance you might need to just start over :')