First: make a new backup of your wallet.dat!
Then: check your addresses on for instance
Blockchair.com to see what the current balance is.
What fee did you use for your transaction? And what "tiny" amount did you send: if it was less than 0.00000546
BTC, it's under the dust limit.
A warning: ignore all "help" you get offered through PM, people have been scammed that way.
If the fee is not equal to the min fee it might still not be relayed by your connected nodes, even if it meeets 546 sats.
Anyway, please make a backup & then slowly think about what the problem might be.
You have lots of options; first, to check if there's actually 1 BTC in your account, open the wallet address in a blockexplorer.
If so, you can do a number of things; export the private key, abandon your current transaction & rebroadcast, etc.
I'm not that great with the GUI, but if you try to list your transactions, (listtransactions), can you find it? If so, try to abandon it and resend.