The same thing happened to me when I first got my 2020 Prusa i3 working. It might actually be a bug in the assembly instructions vs the current kit revision, because I assembled the kit with painstaking care and obedience to the instructions. I'm now very familiar with Marlin and RAMPS, but initial assembly problems such as this are what inspired me to dig deeper.
Now my 2020 machine is in the middle of a super-sizing upgrade with OpenBuilds extrusions and rollers to make it on par with the i3 Mega. My final obstacle in the upgrade is getting the heated bed repaired after it half-died.
In the RepRap 2020 i3 kit, getting it to work unmirrored with a max endstop is an obstacle for people just learning, considering such does not work with the default gdrive firmware. I'd be happy to share my configuration files for the latest Marlin release if anyone needs help. My bed size is the same, but I use OpenBuilds carriages for X and Z movements, increasing my height to 300mm. That being said, the 2020 i3 kit was a wonderful kit to start with in 3d printing, especially because of having to work through issues (teaching moments).