With a lot of mixes like that, between breeds of such disparate sizes, accurately predicting adult size can be difficult, and all too often unethical breeders will tell people what they want to hear. Even in purebred dogs, you will get dogs outside standard size, who wind up smaller or larger than typical.
Your options as I see them are 1) Keep him, and hope he doesn't wind up over your complex's size limit; 2) return him to the breeder; 3) turn him over to a rescue to be rehomed; or 4) rehome him privately, making sure that you neuter him before the new owner takes him home. Another option is to move to a different apartment without a size limit, or even a house with a yard, but that's probably more difficult than any of the other ones.
Your options as I see them are 1) Keep him, and hope he doesn't wind up over your complex's size limit; 2) return him to the breeder; 3) turn him over to a rescue to be rehomed; or 4) rehome him privately, making sure that you neuter him before the new owner takes him home. Another option is to move to a different apartment without a size limit, or even a house with a yard, but that's probably more difficult than any of the other ones.
