normrnd -> normal distribution

I have a quick question: I need to randomly generate
numbers for some real data measurements that I have (i.e.
expand my data for a simulation model). I use normrnd to do
this in matlab. now my question is:

i have a sample that consists of 20 observations and I
would like to create four samples in total (3 randomly
generated plus the original) to test a hypothesis. Would it
be enough to use the original sample of 20 observations to
randomly generate similar sequence of numbers (mean and
standard deviation from the original sample) or I need a
minimum number of samples each with 20 observations to
statistically do that in matlab?

thank you,