I went in to game on my own a got asked if I wanted to pre order a game and I asked to put a £5 deposit on assassins creed 3 and it's a 18 I am 16 they let me pre order it. Can I go and pick up the game on release date by myself or do I need a parent with me?

They should NOT have allowed you to pre-order this title in the first place.
You WILL need an adult to complete the purchase.

Since they were lax asking for ID when they took your deposit, who knows?
But I have a feeling you will need a parent with you. You don't even say where.

Since they were lax asking for ID when they took your deposit, who knows?
But I have a feeling you will need a parent with you. You don't even say where.

The UK most likely. It is five pounds