Im an adult. Needed a Night Guard mold. Dentist used childs mold!?

None of the adult molds would fit on my teeth so the dentist used a childs mold for my top teeth. My teeth are straight there but they are pushed forward so I cannot put on the gaurd without it pushing my front teeth back. Its to uncomfortable but should I keep it??? Should they have found a right adult mold for me because i feel the childs mold is making my teeth more narrow.