plot_2d using latitude and longitude

I am using plot_2d and coast.m to graph Direct Normal Irradiance (DNI) from the TMY3 dataset. I have prepared 4 column vectors with the average DNI for 959 locations for each quarter of the year. However, the gridding doesn't seem to match up. I've used similar code for another project a couple years back and don't know why the lat/lon on this project doesn't allow for proper map size or for the data to be plotted correctly. Each vector is 959x1, if that helps at all.

 %create the spacing for lat/lon to graph
      % create nlat/nlon for proper grid spacing
      nlat = 959;
      nlon = 959;

      % create the degrees for lat and lon
      dlat = 180/nlat;
      dlon = 360/nlon;

      % create the lon and lat variables
      lat = [-90:dlat:90-dlat];
      lon = [-180:dlon:180-dlon];

%produce five images... yearly and four quarters.

      %find the min and max of the q1_dni so it can be plotted
      cmin = min(q1_dni(:));
      cmax = max(q1_dni(:));

      % prepare your arguments for the function
              figure(1)
              variable=q1_dni; % variable you want to plot
              units='Wh/m^2'; % units of your variable
              figure_number=1; % assign a figure number (integer)
              x_axis=lon; % this is the lon vector you created
              y_axis=lat; % this is the lat vector you created
              cmin=cmin; % this is the minimum value you found
              cmax=cmax; % this is the maximum value you found

          % you are ready to plot. use the syntax below to plot
              plot_2d(figure_number,x_axis,y_axis,variable,cmin,cmax,units);