If you don’t have limit switches, you’ll need to manually enter the GCode command (or set a macro) to reset the axis: G92 X0 Y0 will reset them to zero wherever the machine is. Usually if you just position the head at the front left before you power up, that’s good enough.
For the size issue, go to Edit > Machine Settings and look for X Steps per mm, and Y Steps per mm. You’ll need to cut those numbers in half and then possibly fine tune from there. Fixing those will also mean you can double your acceleration numbers again.
Yes, you’re missing something: GRBL. You’ve continued posting in a GRBL thread and not mentioned that you’re now using entirely different firmware (Smoothieware) which stores its config in a file on the SD card. Ray tells me you also have a topic open on the C3D forum for this, so I’ll leave it to them.
