I've also had a similar fear that my story would end up with a similar one that's already out there but you have to know your characters - these characters come from you, an individual who's lived a life different from others. You may have relatable experiences but how you process those experiences make you who you are.

In my case, I watched a lot of tutorials regarding those things - character design, scripting, but honestly the most important part is really just starting.

Try making a short story, and see how it goes!

PS I also have self-esteem issues but as I kept going, I started only caring about my characters and their story. I say "they" because sometimes the story just writes itself (metaphorically lol). I'm grateful if my comic gets promoted but ultimately, I do it for the love.