Well, here's my advice:
Set realistic, achievable goals for your projects.
You say you're not 100% confident in your idea and you don't think your ideas are good enough... but the question then is... "you're not 100% confident in your ideas being good enough to achieve what?"
Like okay, if you're still developing and learning, then maybe you're not ready for a goal like "I want to make something that gets picked up as a Tapas original and made into an anime!" and putting that kind of goal on yourself is a bad idea. Start out with clear, manageable goals like:
"I want to make a series and continue until I have 100 updates"
"I want my novel to have 50,000 words."
"I want to write/draw a complete story"
"I want to make a 12 page comic that I can submit to an anthology"
"I want to make 5 pages of my best sequential art and go to a portfolio viewing with a real editor."
"I want to make a series that can get 100 subs on Tapas without sub-for-sub"
"I want to make a short, self-contained series to test out a totally different style/genre"
"I want to have fun and make friends!"
These are things that you CAN reasonably aim for. If you feel intimidated, it's probably because you're putting way too much pressure on both yourself and your idea to rocket to the big leagues before you're ready.
My past comics usually had aims like "I want to try to place in this national competition" which I sometimes succeeded at, and sometimes didn't, or "I want to make this short comic for this anthology before the deadline", or "I want to show I can do a different genre from the ones I'm known to work in".
I aimed a little too high with my comic and got pretty demoralised because I set myself "get 2000 subs and pitch to be on a Tapas Premium program" as a goal, thinking that was reasonable for an experienced artist, and when the algorithm changed and sub gain slowed a lot for everyone, I felt really bogged down.
Some smart friends seeing the state I was in told me to instead focus on what had been my secondary goal: Complete book 1 (chapters 0-3) so I can make it into a print edition. This was the right call, because Tapas changed things around, scrapped the 2000 sub requirement for premium series, and then not long after I finished chapter 3 (during which I broke 1000 subs) I got an email from Tapas inviting me to a Premium program. If I'd quit because my idea "isn't good enough" to achieve the ridiculous goal I'd set myself, I wouldn't have achieved it! I'm thankful to my friends for telling me to just focus on making a fun and solid 150+ page comic to the best of my ability as my goal and just believing in my ability to do that.
Pace yourself! It's okay for your goal to just be "I want to challenge myself to draw/write things I struggle with and learn from the experience" or "I want to write a long enough short story to get a really thorough critique from more experienced creators." Your stories don't all need to be top-drawer ideas. Some of them can be silly little things you just make for fun, or to explore a style or idea... and sometimes those are actually the ones that unexpectedly blow up!
Remember; your story doesn't have to change the world or be the greatest ever, it just has to entertain people, so focus on that first.