flexible funding means that you will get the money even if you don't reach your goal. Usually if the goal is not reached no one gets a thing because there was not enough to go to production.
Yours is a small amount goal but still people backing you have no warranty of their money going towards the product they are promised because often the campaign founders will retract from the orders because there is not enough funding to do a production run.
So yeah, it's a mistake to do flexible funding even at small amounts because backers will feel their money will go nowhere if not enough is raised and they can't get their money back nor the product.