FFT from CSV file

I tried fft on channel 2 of the CSV file above. the signal is 20 ms and 20000 data is taken. I have followed the fft steps provided but the frequency signal does not come out correctly. Where my frequency signal is received around 10-15 hz because the input channel 2 is received from afg while the input frequency is only 10-15hz. Did I make a mistake to enter the code for channel 2 ?? Besides that I ask for channel 1 whether the code I input is the same as channel 2 because channel 1 is a sensor that I measure on the sound where the input frequency I input on the sound is the same where the frequency I use is 10-15 hz.