You're measuring how many standard deviations from the mean a given value is. Certainly values can be many standard deviations from the mean. Even for data with a normal distribution, we expect about $5\%$ of the observations to be more than $2$ standard deviations from the mean, and we expect $32\%$ of the observations to be more than $1$ standard deviation from the mean.
Therefore, it is not at all concerning that you have values more than $1$.
As far as values less than $0$ go, all that means is that you have a value less than the mean. This is common. (While it can happen, consider how to have a data set where no values are less than the mean.)
As Sammy mentioned mere seconds before I posted, be sure to use the mean and standard deviation from your training data when you transform the test and validation data.