thoughts on relying on tutorials for bg art

im a new artist and solo dev whose basically starting from scratch learning to draw for my vn. im giving myself quite a while to develop the skills for faces, but im also in grad school w two jobs so i can't put that much time into it. while my art for sprites is progressing but not quite where i want it, the backgrounds ive drawn so far are game ready in my view.

im wondering if there's something unethical about using art ive drawn based on tutorials for a paid game. i make them my own in small ways and spend hours painting them, but the general design is not my idea. can i use these in a paid game or do i have to wait until i can conceive of and execute my own background layouts ?