I have reversed the charge for the accidental purchase you reported. You will see a credit of $4.99, plus any applicable taxes, in three to five business days. Please note that the iTunes Store Terms of Sale state that all sales are final, so this is a one-time exception.
The best way to avoid unintentional purchases is to use the Shopping Cart. That way, you can consolidate and review your selections carefully and buy them when you're ready. Here's how to use the Shopping Cart: