Issue with geom_line function


I have a data set from a measurement. It has 117 rows and 26 columns as shown in the attached image(my_data).

I'm trying to plot Wavelength (nm) in x-axis and ph13 to ph1 in y-axis using geom_line function. But as you can see in right corner of the image, the plot is not good. As an example I have also attached an image of how plot should look (Expected_plot).

How can I solve this problem. Please help me.!