Time for a reality check. Your lack of confidence in your work is hurting your image and your chances at success.
Self-doubt is nothing new for the field of writing, any more than it is to the other creative fields, like music and art, but it is my experience that writers are more apt to discuss it than musicians or artists. I think there is a time and a place for participating in self-doubt about your work, but that time should wane when you graduate from high school and end with college. (If you started writing later in life, I'll give you a little more leeway.)
Why do I say it should end with college? Because the number of people who give a damn about your self-doubt shrinks exponentially when you leave the safety net of a college setting. Sure, you can find plenty of forums where you can commiserate with other writers about self-doubt, but I can tell you that your readers don't want to hear about it, and neither do agents or editors. It's a huge turn-off.
Case in point: “I remember the day I walked into Barnes & Noble and saw the books on the shelf for the first time, I felt embarrassed. I didn’t feel like my books were worthy enough to be displayed next to ‘real’ authors.” - Colleen Hoover talking about her book Slammed in a recent Book Life piece
How many of you think that sounds sexy, cute, or endearingly quirky, coming from a best-selling author? If you think instead that it sounds absolutely ridiculous, I agree. If I read romance novels, I would think twice about reading one of hers, because she thinks it's not worthy to be read. So...why should I want to read it now? Trust me, your readers aren't any different.
If you love writing, and you want to do it professionally now or in the future, do yourself a favor and take a long look in the mirror. Ask yourself if you want to be taken seriously as a writer. If the answer is yes, then stop asking yourself if you're a good writer.
It's perfectly ok to recognize that some aspects of your work need improvement, like being too wordy or using too much passive voice. Every writer has had to improve on something. No one pops out of the womb a perfect writer. NO ONE. Writing is a craft like any other. If you work hard at it, you can overcome almost any writing difficulty.
But, the moment you ask yourself or ask someone else if you're any good as a writer, you've degraded your own credibility. So, stop degrading yourself and go be a writer already. You'll do just fine!