Ok, so I'm assuming that the transaction that you sent to your friend is showing in your transaction list (as unconfirmed)? If you are using 0.14.1, you should be able to right click on the transaction in the transaction list and select "Abandon Transaction".

If that doesn't work, then I would suggest shutting down your Bitcoin Core client... and restarting it using the "-zapwallettxes" commandline option... This will remove all unconfirmed transactions from your wallet, which, in theory, should then mean that your balance reflects what is in your wallet.

Having said that, if you wallet is not synced, and there are transactions on that address AFTER the last block that has been synced, you may get an incorrect balance.

I take it you still haven't been able to get the sync working? What version of the Bitcoin Core client are you using?

EDIT: Actually, it probably won't really matter... if you can see your addresses, proper balance or not... you can still dump the private keys... once you import the private keys into another wallet, that wallet should be able to scan the blockchain and get the correct transaction history and balance for your address.