If you feel like you are demiromantic, then you are demiromantic.
When it comes to romantic/sexual orientations outside of the well-known few (exclusively gay, exclusively straight, exclusively bi, ace, etc.), feelings towards such labels tend to be 50/50. In the end, people will tell you THEIR truth, and what THEY believe to be correct. If they don't believe in the demiromantic orientation, they will tell you "no, that isn't a thing." Alternatively, if they do believe in it, they will tell you "yes, that is a thing." It's all subjective and, most of the time, they are answering from their own beliefs and not exactly with any true basis.
This is your identity, your orientation, not anyone else's. Don't rely on someone else's truth to be your truth. IF you feel like you are demiromantic, and that is a label that you feel most comfortable with, then you are demiromantic -- don't let anyone tell you otherwise.
Additionally, if you don't feel comfortable with labels in general, don't feel like you have to label yourself. You do what makes you most comfortable, and identify as what makes you feel most comfortable.
So, to answer your question, let me ask you some questions. Do YOU think it is a thing? Do YOU find comfort in the label? Do YOU identify with the label?
Only you can answer this question.