Images are showing up too large and pixelated

When I add my product image, I am linking it to a thumbnail image. The image is 107x150px for the Portrait images. Those are showing up much larger and pixilated.
The landscape images are linked to images 150x107px and they are coming out perfect.
I don’t understand what I am doing wrong.
I would like all of my items in the store to be thumbnails.
https://www.angelmadejewelry.com/dir/store/
Thank you
Angie

http://wordpress.org/plugins/simple-e-commerce-shopping-cart/