Universal Heatplate from old 3D Printer

First of all: I'm not an expert in PCB design or electronics so I'm open to feedback what I can do better :)

I needed a hotplate for a phone repair, but just had an old 3D Printer Hotbed laying around.
So I thought, I give it a new purpose.

The Hotplate can reach temperatures up to 90°C.

The PCB Design is based on standard perf board, so it's easier to do at home.

The Hotbed used was in my case a 12V one from a FreeSculpt 3D ex1.

Parts List:
Hardware:
1x 12V Hotbed from 3D Printer
1x "3D- Freunde" V2 Mosfet (https://amzn.to/3bNbzUJ) (Others will work too)
1x 12V 5A Powersupply (https://amzn.to/2JrzVXV)
1x Another Arduino board for programming the Pro Mini
Xx Some Cables and Plugs for connections to Hotplate, etc.

Components for PCB: (In the Thing files you will find a more detailed parts list)
1x 90x58mm perf board
1x Arduino Pro Mini (3.3V 8Mhz)
1x 7-Segment Display
1x DC-Input Jack
1x PNP Transistor S8050
1x 3x2 Male Header
1x 1x2 Male Header
8x 100 Ohm Resistor
1x 15k Ohm Resistor
1x Screwterminal
1x Hesai Buck Converter
1x Tactile Switch (12x12mm in my case)
Xx Copper wire as jumpers

Screws:
6x M3 10-15mm
3x M2 4mm
4x M3 3mm
3x M2 washers