Known quality control issue with 10234 Sydney Opera House?
You seem to imply you built some of the structures symmetrically; however, by looking at the building instructions, I notice they are not: the subpart starting at page 37 of book 3 uses 7 wedges in total, while the opposite one on page 48 uses only 6.

While missing parts do happen (and are usually solved very diligently by the customer service, as said in other questions on the subject), it's always worth double-checking if the instructions were followed correctly, especially in such a huge model.