Simple Digital Oscilloscope

The requirements
are to build an oscilloscope (or oscilloscope expansion board) that meets the following basic specifications:
±10V dual-channel 2M sampling rate or higher, 20k bandwidth,
sine wave peak-to-peak measurement error no greater than 5%,
range switching function (switching control method is not limited)
, stable triggering, no obvious slippage,
frequency measurement error no greater than 5%
, ±4V 20k output, square wave, triangle wave, sine wave
, sine wave, and square wave peak-to-peak error no greater than 15% .
The schematic design is
based on the official schematic from Hardwood Classroom, with modifications. Below are images of the schematics for each part.
Important Notes:
I encountered many difficulties during the construction process, such as soldering. This was one of the few times I soldered surface mount components, so I was very slow at first, but I gradually mastered the techniques.
For example: 1. Don't add too much solder paste. 2. Buy a small blade tip for the soldering iron, as this is more conducive to soldering surface mount components. 3. Be careful to avoid cold solder joints. 4. Be extra careful with components with many pins. I was particularly impressed by the screen socket; buy several to avoid solder bridging. 5. Don't set the soldering iron temperature too high. Also, regarding the purchase process, I checked the BOM list item by item and changed it to JLCPCB.
During testing, I encountered many problems, such as incorrect resistor values, cold solder joints, and short circuits. I checked each problem step by step with a multimeter and finally found the error.