It's possible that your transaction is a double spend because you are not synced. This would make your transaction invalid and thus rejected.

You cannot cancel a transaction. Once it is broadcast, you cannot abort it.

However, you can remove the transaction from your wallet and resend it. First you need to sync your wallet. You can enable pruning to save space.

To enable pruning, add
To the bitcoin.conf file in your data directory.

Then follow the instructions at http://www.achow101.com/2016/07/Bitcoin-Core-Troubleshooting#stuck-tx to fix your problem.