If your subjects are reflective, then greenscreen probably isn't the best technique to use for background removal. A black background might prove more effective. If there is green reflected on your object, it will be removed along with all the other green when you key. You could use a mask to keep those areas from being removed, but you will still end up with green reflections on the object.
If its just a bit of ambient reflected green along the edges of your subject, that's different, and can be dealt with, but if you have an actual reflective subject, then greenscreen is going to prove problematic. If you can upload the original image to www.imageshack.us
or some other webspace and give us a link, we may be able to offer more specific suggestions.
Use the Canvas Size to change the size of the canvas area. Setting it to As Foreground will automatically make it match the size of the foreground you import. Otherwise, use the Position controls to adjust the size so it fits into your desired canvas size.
Also, I've deleted the second topic you started asking this same question, as having two threads discussing it is unneccessary. Please don't double-post in the future. Thanks.