Hi,
Spend more time for the PCB layout.
A nowadays layout is not just connecting signals from A to B.
Make the whole bottom layer GROUND.
Move parts so that wiring becomes more easy.
Place decoupling capacitors next to the IC´s supply pins.
Then place via next to the part pins to connect GND.
Then route the most important signals first, then the less important signals.
Check your layout.
***
In your current layout you several times unnecessarily split the GND plane. Why?
See this:
View attachment 151435
The red area is GND and the red wire is GND, but the red wire splits the GND plane into pieces.
***
A GND plane is essential with high frequency signals and with high (pulsed) currents. Now in your case the device with the highest power consumption is the SIM800C and it is the device with the highest frequency...but you completely refused to use a GND plane there. A no-go in my eyes.
Don´t confuse yourself with irritating signal names: signal LED1 goes to LED3; signal LED2 goes to LED4.
LM2576 datasheet includes a section: "Layout guidelines". Don´t ignore it. There´s a good reason why they wrote this chapter.
Klaus