Keeping values in a matrix in a nested loop

Hello, don't think my problem has been answered..i'm relatively new to MATLAB.

Basically i want to create matrix where each row is repeated the number of times as the value in the 3rd column for each row. i have set that part up in a loop and it works, what i'm having trouble with is keeping the data each time the loop iterates. There's a problem with the indexes but i can't quite place it for matrix 'B'. Error= Subscripted assignment dimension mismatch. Here's part of my code with the Loops:

 %G1 is the original matrix (3457x3)
 % N is a matrix with all the values in column 3 of G1

 for g1= 1:length(G1);

 g2= G1(g1,[1 2 3]); %g2 = the row of G1 corresponding to the index

 for n=1:length(N);

 n1= N(n);

    g4= intersect(g2, n1); %g4 gets value i need to repmat with

if isempty(g4);  %sometimes g4 doesn't match g2
    continue
else
end

    jg= find(ismember(G1,g2,'rows')); %finds all indexes in big matrix with same row pattern.
    g4= round(g4, integer);
    g5= repmat(g2, size(jg),1);

    Save= repmat(g5, g4,1);   
    B(1:length(Save), end+1)= Save ;

    n=n+1;
end

    g1=g1+1;
end

I have used B(1:length(Save), end+1) before in a nested loop and that seemed to work. i have also tried B(n,:) and subsequent other solutions from other questions. Any suggestions would be great!

EDIT: I have solved the problem but i had to pre-allocate a 3 dimensional matrix, if anyone knows how to keep a two dimensional matrix the problem still stands, here is the revised code:

 clear all

 S= load('extra_spike_mat');
 St= S.extra_spike_mat;
 index=1;
 integer= 0;

 St1= St;
 St1(any(St==0,2),:)= []; %removes rows with zeros

 %repeat row the number of times as spike rate
 N= St1(:,3); %spike rates
 St3= St1(:,[1 2]); %amp and freqs
 index= 1;
 max_nrep= max(N);
 max_nrep= round(max_nrep);
 nrows= numel(St1);
 B=zeros(nrows, max_nrep,3);
 Nunique = unique(N);

 for st1= 1:length(St1);
    St2= St1(st1,3);
     nrep= round(St2);      

    Vect= repmat(St1(st1,:), nrep,1);
    %size(Vect)

    B(st1, 1:nrep, :) = Vect;

   % index=index+1;
    st1=st1+1;
 end

All i have to do is remove the zeros, but being a noob this is harder for me to deal with.