I have designed for years, there are public domain blocks which are not copywrited.
When designinng a quilt, it is ok to use them,, & tweak with your own input.
For instance,, I used duck & duckings block,, added sashing, but then added an. Embroidered block which I digitized myself. It was my own quilt design & I marketed it.
When you enter a contest,, they usually give very detailed requirements, dos & don' ts. Check their info out, usually they only state that you. can' t use copywrited material.
When I have designed for fabric companies, they only require that you use a certain fabric line which they provide. Then your design is judged against other participants & they choose the best design for their fabric line.