64-QAM Modulation and Demodulation

Here's example of Quadrature Amplitude Modulation with Bit Inputs:

M = 64;
bitsPerSym = log2(M);
x = randi([0 1],10*bitsPerSym,1); % x is input variable
% modulation
y = qammod(x,M,'bin','InputType','bit','OutputDataType', ...
    numerictype(1,16,10));
% demodulation
z = qamdemod(y,M,'bin','OutputType','bit');
s = isequal(x,double(z))

The theory of 64 QAM is to transmit data with 8 bits per symbol.

My question, if the data I generate is not a multiple of 8 (like 61 bits), how can I do 64 QAM transmission?