Is it shorter than it was when you took it out of the press? If so, the curd may be settling, rather than puffing up, even though it is wider than the mold now.
Cheese that is moist will do that - my Colby ends up being about 8 inches wide and three inches tall, although it starts out 6 inches wide and about 4-5 inches tall. The moisture in the curds mean that the size/shape isn't as stable when you take it out of the press as a dryer cheese would be.
If that isn't the case, don't throw it out unless it smells bad. If it smells yeasty, you can eat it young. It won't be the same, but not inedible.
Yeast and other beasties are in the air all the time, so it is difficult to avoid them completely.