You really messed on on find. find() does not return x and y in that order -- it returns row and column (y and x) in that order. After that, just use min and max
[node_y, node_x] = find(endpoints==1); %getting the x and y coordinates of the endpoints in
%node_x and node_y respectively
% Get top row which is the smallest y value
yTopRow = min(node_y);
% Get bottom row which is the largest y value
yBottomRow = max(node_y);
% Get left column which is the smallest x value
xLeftColumn = min(node_x);
% Get right column which is the largest x value
xRightColumn = max(node_x);
