iTunes preordered album

I recently preordered an album with a total cost of $9.99. Initially, three songs were available in advance and I was charged $4.05 for these. A fourth song subsequently became available and I was charged $1.35. Now I have been charged $10.49 for the remainder of the songs. So I have paid $15.89 for $9.99 album. Can someone explain this to me?

Thank you