The dictionary definition is:
‘noun
One, such as a painter, sculptor, or writer, who is able by virtue of imagination and talent or skill to create works of aesthetic value, especially in the fine arts.
A person whose work shows exceptional creative ability or skill.
"You are an artist in the kitchen."
One, such as an actor or singer, who works in the performing arts.
One who is adept at an activity, especially one involving trickery or deceit. "a con artist."
One who practices some mechanic art or craft; an artisan. Similar: artisan.
One who professes and practices an art in which science and taste preside over the manual execution.
One who shows trained skill or rare taste in any manual art or occupation.
An artful person; a schemer. Similar: schemer.
A person who creates art.’
I don't see anything pretentious in calling yourself an artist. If you do create art then you're an artist.
Does playing ‘Sex on Fire’ down the Dog and Duck on a Saturday evening make you an artist? Probably not, but if you're writing lyrics and composing your original music, then yes.