STM32F103C8T6 custom design check
I recommend a pull-up resistor from NRST to VDD and a feritte bead + 100nF + 1uF bypass capacitor to decouble VDDA from VDD when you use your ADC.  Further, you should implement a jumper for your BOOT0 pin, such that you can choose between VDD and GND for changing the boot configuration.



For your PCB design, I recommend to use more vias to connect the top and the bottom GND layer. Additionally, you should add some mounting holes. You can also put all your bypass capacitor under the board, normally this way you have the least distance from VDD to GND and your other GPIOs have more space.

Edit: I see that you have a bottom VDD Layer, you don't need this on a 2 layer pcb. Just use one GND layer at the bottom and separate traces for VDD only where needed.