According to what I read in the API docs for creating a fulfillment, I can specify 1 tracking number and all of the items on the order will be marked as shipped so I won't have to add any line item data.
http://docs.shopify.com/api/fulfillment#create
The fulfillment data that I am submitting is: { "fulfillment":{"tracking_number":"9400110200828012451152"}}
Is there more info that I need to add?