I designed a set of furniture. What does the instructor mean by not applying for a patent to participate in the competition? Just not doing well? Please answer if you know.

No, that is to say, if you don't apply for a patent, it will be meaningless to participate in the competition. First of all, you compete to get good grades, otherwise you don't have to compete. Once you get good grades, the furniture you designed will certainly be imitated by others, because you didn't apply for patent protection, and winning the prize is meaningless.