Hello,
The frequency reading in the bottom right is the trigger frequency and will not show a frequency under 10Hz. To get the correct measurement for your signal, you can push the Measure button and then add a Frequency measurement for the channel in question. When you have the correct channel selected, push the Multipurpose knob to add the measurement and it will show on the bottom left side of the screen.
Just so I am clear, the amplitude you are changing is the amplitude of the signal and not the vertical scale, correct? The voltage value in the bottom left next to the channel badge is for the vertical scale. Are you using a measurement to find the voltage value? If not, you can add an Amplitude measurement from the same menu as above.