Hi Friends, Gurus, Experts,

I was trying a BTC send transaction for the first time, so sent 5$ worth BTC, I didn't want to pay higher fees and I was ok to wait for a few hours / days for transactions to confirm, so I chose lowest possible fee of around 250 satoshis. 
The transaction remained unconfirmed for days, I kept on checking it once in a while, then  On 5th or 6th day,
I see following message

Transaction invalid: some outputs that it attempts to spend have been already spent or are no longer valid.

what happens in this case ?
How do I recover my 5$ worth of BTC

Appreciate any help / suggestion.

Thanks and regards,