I designed a silicone mold and I want the factory to make it. Mold making is very expensive, but is there any way I can ensure that the factory doesn’t use the mold I made to make it for others?

If the product is released late in the market, it is impossible not to be plagiarized. It is useless to print a LOGO on the mold. All you can do is sign a confidentiality agreement. But this thing cannot guarantee that it will not be plagiarized at all. In fact, this is meaningless because as soon as your product appears on the market, others can copy it.