How do I get better?

I seem to act really good when it's over-the-board, but every time I play online, I am terrible! Is there like a gambit for black that can help me overcome this? (I know as white I can do Queen's Gambit.)

Perhaps the Stafford Gambit? (I'd recommend the following video for looking at openings for black: DOMINATE with Black: Opening Tier List)

Don't even bother bud. Something is WRONG with this site. I lost all my ELO past two days went from 1200 to sub 1100. None of the players on here play fairly. These guys aren't playing at their rating and it's not you, it's the lack of regulation on here and a bad system. Go play OTB and find your real rating there. I've had enough of losers in sketchy countries suddenly winning the game after I'm up 10+ points. Hanging a queen on move 3, but not resigning and then winning the game. Yep. Totally makes sense. And then report them and what do they do? Nothing. Bunch of losers on here that's it. Losers and people who had chess coaches and have high ratings because they learned the proper way how to play.

Learn and apply the most important principles of chess. - (core of my teaching)
Always blunder-check your moves.
Solve tactics in the right way.
Analyze your games.
Study games of strong players.
Learn how to be more psychologically resilient.
Work on your time management skills.
Get a coach if you can.

Well, I don’t think my opponents will fall for that trap.

Trust your OTB-experiences. I also get much better results IRL than online. They are all Bots to me, anyway LoL