Why are my bitcoin transactions going to 2 addresses
When you have to pay a transction from an address that is only part of the total balance of that address the program you use for managing your wallet (in your case bitcoin core) sends to the destination the amount that you wanted (in your case 0.003), and the rest is sent back to another address of your own (minus the fee).

This is because for how transactions are designed in bitcoin when you make an outgoing transaction from an address you cannot use just a part of it. All of it must be spent in transaction (towards 1 or more addresses) and the rest goes to the miner as a fee.