Try importing your texture as an image rather than a texture. You’ll find that you can simply drag it bigger…like you were using the rectangle tool. You can even tweak it later to fine-tune the scale. When you are happy that it’s the correct size then select and explode it.
You can either use the exploded image itself as the surface upon which you want to paint it, or try projecting it from the imported image to the prepared surface.
I just posted a tutorial on how to bring in textures the correct size.
http://forums.sketchup.com/t/how-to-import-materials-and-how-to-add-to-create-material-libraries/28174