OK. You have to paint the undersides again.But apply a thin coat.Also paint the nose (air intake) like you can see in the pic I posted a few posts above.At the area you have to apply much paint because it was painted there partially only.But this time make the blue paint lighter, add much more of white OK?
Oh and another tip.... when you have already painted a surface of wing for instance but you need to correct it at any area don't change the brush moving direction. For example you was moving the brush like I told and showed you..I mean from the middle to edges.So you must not apply a paint from the wing tip to itsa root for instance It is the reason of appearing of smudges..Do you grasp?
Harry when you paint a model undersides hold it in the way I told you.Also the way of holdning works fine if you are going to show the just painted undersides..
When you start painting of top surfaces you will have to hold it in another way.But about it I'll tell you later.