I see nothing wrong with it. Most people buy the books because they want the pattern or patterns and cannot figure it out without the book or want to remember the quilt the way they saw it. You certainly don't have to buy a book or pattern to make every quilt you like. So many that I have made were just by what I wanted to do.
Please don't worry about it. If you do decide to show it, they usually ask what was your inspiration and you can tell them. And if you decide to claim it as your own and sell it - then you will more than likely have problems.