Paul sorry to hear that all this happened at once, as said, should have been more careful and payin more attention. i got points for speedin in my old yoke but they're gone now and i learned my lesson and kept meself out of danger.
Really depends on the guard ye get, he could be a prikc about it or else he might be ok. As said you should check (With a licenced driver) to see if there are signs for the motorway when you came onto it. not quite sure bout the n4 but with all the roadworks goin on i dont know if they've put up signs to say the rules bout the road ie no L plates etc, so you might get off there.
Invest in hands free kit, even if it is the headphones one, very handy and save ye getin 2 points.
Hope they dont go too hard on ye lad. keep informed,
Paddy