The first argument to subplot needs to be 2 because there are 2 rows. The layout is this:
1 2
3 4
For the first two plots, the second argument is 2 because there are 2 columns, and the third argument will be 1 and 2.
For the next row, you also have 2 rows. The layout for subplot(2, 3,n) is this
1 2 3
4 5 6
So you need to put the images into slots 4, 5, and 6 because you want them in the second row, not the first row. Here is the corrected code.
subplot(2,2,1)
% imshow(fig1)
subplot(2,2,2)
% imshow(fig2)
subplot(2,3,4)
% imshow(fig3)
subplot(2,3,5)
% imshow(fig4)
subplot(2,3,6)
% imshow(fig5)
