Your itemList is currently made of exactly one item; that is because the default particle cardinality is 1 (minOccurs = maxOccurs = 1).
If you wish more than one, then you need to add maxOccurs attribute with the appropriate number; for unlimited, use maxOccurs="unbounded"... like so:
<element name="item" type="co:itemType" maxOccurs="unbounded"/>