I copied the error message, this is what is says
Arduino: 1.8.10 (Windows 10), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"
Sketch uses 2966 bytes (1%) of program storage space. Maximum is 253952 bytes.
Global variables use 220 bytes (2%) of dynamic memory, leaving 7972 bytes for local variables. Maximum is 8192 bytes.
C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avrdude -CC:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf -v -patmega2560 -cwiring -PCOM3 -b115200 -D -Uflash:w:C:\Users\Andreea\AppData\Local\Temp\arduino_build_400302/flex_snesor_angle_measure.ino.hex:i
avrdude: Version 6.3-20190619
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch
System wide configuration file is "C:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf"
Using Port : COM3
Using Programmer : wiring
Overriding Baud Rate : 115200
avrdude: ser_open(): can't open device "\.\COM3": Access is denied.
avrdude: ser_drain(): read error: The handle is invalid.
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
the selected serial port avrdude: stk500_send(): failed to send command to serial port
does not exist or your board is not connected
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: ser_send(): write error: sorry no info avail
avrdude: stk500_send(): failed to send command to serial port
avrdude: ser_recv(): read error: The handle is invalid.
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer
avrdude done. Thank you.
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.