I'm not sure writers ever get over such insecurities, Ana.
I've been writing for so many years but still find it difficult to stay in this skin at times.
If it's not the "who do I think I am," and I like what I wrote, I still find it difficult to promote it.
I'm currently reading William Zinsser's "On writing well". He was a teacher and often references the talks he had with his students.
When one would tell him, "who am I to write this", he would ask, "Who are you not to write this? You're the only one in the world who can write it exactly this way, and this is precisely why you should write it" :D
I know, I know, easier said than done...
Would love to meet whenever we get the chance :)