i was expecting you can come to my cocktail party.

主句：i was expecting 是过去进行时态,表示说话前“正期待着”
宾语从句：you can come to my cocktail party。你能够来参加我们的鸡尾酒会。
分析：根据从句中表示现在的 can,说明 was expecting 是刚才还在进行着的行为。
翻译：我（刚刚）还盼着你能来参加我们的鸡尾酒会来着。