Write the operating system by yourself

Write the operating system-general Linux technology-Linux programming and kernel information by yourself. The following is a detailed description. I completed pmtest2.com according to the steps in the book. Are you sure there is no error?
However, during debugging, The LABEL_GDT offset is found to be 103,
Prepare for loading GDTR
Xoreax, eax
Movax, ds
Shleax, 4
Addeax, LABEL_GDT; eax <-gdt base address when executed here, the LABEL_GDT offset is changed to 104
Mov dword [GdtPtr + 2], eax; [GdtPtr + 2] <-gdt base address

When lgdt [GdtPtr] is executed, the debugging will exit. I really don't know what's going on. Please help me.