I understand, and it's not a dumb feeling. I write fantasy, and I try to steer away from a lot of the cliché plots and twists to avoid being accused of ripping someone off. However, sometimes the simplest, most classic stories are the ones you want to tell, even if its only with your own characters, or within your own setting. It's a crummy feeling, thinking that you can't do something because someone drew or wrote or even said something earlier on, whether that be a classic like Beowulf or some obscure sketch you remember seeing somewhere and now makes you question if your idea is even your idea at all.
Put that behind you. I know it's a blunt and oversimplified answer, but it's the only way I have found to deal with this appropriately. Like eishiya said in the comments below, your style is unique, and no one has seen what you have to contribute to the story. Heck, there's a reason why a lot of great movies and TV shows have a few writers behind them, and why joint efforts are so popular here on dA.
So draw what you want to draw. Don't let anyone stop you, including yourself.
if you want to draw it, draw it
the only change is the style and author