The design of the entrance is terrible.
The line should be aligned with the cursor of channel 1 yellow or 2 blue. (putting a photo of the trigger cursor here is pointless - yes, I know there is a small inaccuracy, maybe I'll fix it one day)
To align the channel lines:
A basic calibration must be performed through the menu. (you can do this whenever you want, nothing is required.) You should do this every time you see a deviation of the line from the channel cursor. (you should ALWAYS do this calibration before calibrating the input dividers and calibrating the DC offset)
The center line (channel lines) is shifted by heating the oscilloscope and discharging the battery. Therefore, there is a possibility of basic calibration.
In the DC mode, it is more complicated with the centering of the channel lines.
(however, you didn't put the photo I asked for - 3V signal with 0V offset + photo of diagnostic screen)
If any DC offset is present, it will be recalculated to shift the line from the channel cursor. For example, my cheap Chinese generator does not have a 0V offset on the output when set to 0V offset !!!!
If you try basic calibration (disconnect cables, probes from inputs), the lines should align. In AC mode for sure.
In the photo I see DC offset=6, this can cause a shift, the output of your generator may not give 0V offset, try to connect the signal to the oscilloscope through a 100n capacitor, and press autosetup again, if the lines align.