预测图与观测图具有对角线和偏差

I am trying to plot predictions vs observations in a scatter plot showing the predicted values in x and the observed in y, so a perfect fit should be shown in the diagonal. Is there any way to plot that diagonal in excel as a line, so it is easier to see if the result is close to the ideal? Also, my model has a standard error that I would also like to show as upper and lower line. Something like this: I am trying to plot predictions vs observations