1. Copy the transaction ID from the wallet transaction tab (click on the transaction and copy the ID)
2. Open your web browser and go to the Veil explorer (https://explorer.veil-project.com), paste the transaction ID (TXID) in the explorer and see if the transaction is visible on the explorer.
3. If the transaction is visible in explorer the transaction might need to confirm before being fully visible in your wallet. If the transaction is not found go to step 4.
4. Open the debug console and type:
abandontransaction <TXID-from-step-3>
If the command succeeds it will return Null, and your coins should be immediately be back in your balance.
If the abandontransaction returns error Transaction not eligible for abandonment (code -5) go to the next step.
In debug console type:
resendwallettransactions
If the TXID is in the output of this command it should be resent and rebroadcasted to the network.
If nothing worked then you may import your wallet from seed words which makes a clean Veil directory with a new wallet.dat file.
However, if you do some other spends you may find that suddenly your original spend gets confirmed, so do not resort to starting over from your seed words on the same day. It will very likely fix itself over time.