I got the Eldritch Invocations called "Book of Ancient Secrets" and according the books it says:

"You can now inscribe magical rituals in your Book of Shadows. Choose two 1st-level spells that have the ritual tag from any class’s spell list (the two needn’t be from the same list)." 

Yet, I have been able to add 10 spells to the book already. Is this broken? 

As the second paragraph of the invocation points out, you're able to add more ritual spells to the book.

So you dont use those places when you first get it? How do I take off all the extra spells I have now?

Quote from xangpow >>

So you dont use those places when you first get it? How do I take off all the extra spells I have now?

 You can set those selections back to the "Choose an Option" at the top of the list.