Hi
I am new to 3D printing have a problem and need some help.
I have a 10” Prusa and it is printing well but, the problem I am having are the prints are not in the center of the bed. I have loaded Marlin_RAMPS_EPCOS_i3v10 firmare and checked

#define X_MAX_POS 250
#define X_MIN_POS 0
#define Y_MAX_POS 250
#define Y_MIN_POS 0
#define Z_MAX_POS 250
#define Z_MIN_POS 0

Slice3r 1.2.6 and 1.1.7 bed size are set to X250 Y250 Point Center X125 Y125
Ponterface 2014.08.01 width 250 Depth 250

When I print it centers at X125 Y225 my center should be X100 Y200

When I set Slice3r to X200 y200 it prints in the center.
To me it looks like Marlin thinks this is a 8 inch bed and not 10.
As a side note I did load Marlin for a 8 inch by mistake, could it be it is not over writing the 8” size.
Is there a way of testing this or factory resting the board.
Any advice appreciated