How can I get my hair extensions to fit my hair better?

I got new hair extensions. Not the ones that already have the clips in them, that are like - 90 bucks. The ones that come with the track on the top, and you sew the clips on, simple as that. The case says that they are 10 inches long, and when you see them through the case, they look like they add enough length to come down right under my breast. When i opened the pack after i got home, the extensions were thin and a lot shorter than they look. Theres a lot of left over extension, and i was wondering if anyone knew how to make them look thicker, and longer? When i put them in my hair, you can barely see them, because they are so short. Please help me! thank you!