It does not matter what is the size of the output of your random number generator. You have to concatenate the outputs of your generator in order to test with the NIST test. See for example this python code:
import struct
v=7;
f=open('rnd2.bin','wb');
for i in range(124&255))
The output is 1 byte in every iteration. The output is concatenated and put into a file rnd2.bin. After that NIST suite can be used to test the output of the generator.
Surprisingly this small python program passes all the tests in the NIST suite.