Fixed it

GDT_table:
    db GDT_end - GDT_start - 1
    db GDT_start

as you can see here.. I defined 2 bytes in the GDT_table but thats not what the CPU expects.. it expects a 6 bytes but of course I didn't know that..

anyways the fix was:

GDT_table:
    dw GDT_end - GDT_start - 1
    dd GDT_start