[Help filling in bits that magic wand won't do??? HELP!]

Yeah I tried the tutorial and far too hard for a newbie also I have adjusted the tolerance and I still getthe gaps/white marks etc etc!

[Help filling in bits that magic wand won't do??? HELP!]

I am new to paint.net but loving it's features!

However, I keep coming across the following problem.

Basically, If I use the magic wand to fill in or auto adjust a sky etc I find it leaves bits out that really show up and I can't find a way to get them to match the picture, as you will see in the image below that I am working on.

As you can see with the trees on the left and in the centre of the picture the just stay white. I try and fill them in with magic wand and it either uses an area too big or miles to small! I hope someone can help!

Thanks

http://i44.tinypic.com/2jctqgh.jpg