Shipping multiple items - advice please?

Hello, I've received an order of multiple items, but the shipping method has calculated by the combined weight and not the size nor destination (UK to USA) so I've come a cropper and undercharged drastically. I mean... drastically. Obviously I'll have to take the hit on this one, but - how do I stop it happening again?
I want to be able to ship multiple items anywhere globally, from UK... is that possible?
Jon

Ultimate Shipping can do this. Take a look a the "dropshipping" example on this page:

http://www.getclearthinking.com/ultimate-shipping

Feel free to take a look at the screenshots and demo site, and if you're interested let me know at www.getclearthinking.com/contact if you have any further questions.