B757 FLC APPARENTLY INCORRECTLY INPUT XING RESTR; OVERSHOOTING INTXN ALT AND ARE CHALLENGED BY A80.

Narrative

I WAS THE CAPT OF FLT FROM SLC TO ATL. AFTER RADAR VECTORS FOR ARR SEQUENCE; WE WERE CLRED TO RMG AND THE RMG ARR TO ATL. WE WERE CLRED TO CROSS ERLIN INTXN AT 13000 FT MSL AT 250 KTS AND THEN DSND TO 10000 FT. THE FO WAS FLYING AND ALL SEEMED NORMAL UNTIL THE APCH CTLR SAID 'WHERE ARE YOU GOING?' I LOOKED AT THE EFIS MAP AND REALIZED THE ERLIN WAYPOINT WAS STILL RED (IE; THE ACTIVE WAYPOINT AND WE HAD NOT YET CROSSED IT) SO I PUSHED THE ALT HOLD BUTTON TO STOP THE DSCNT. I CONFIRMED TO THE CTLR THAT WE DSNDED EARLY AND OUR ALT WAS 11500-12000 FT AND WE WOULD CLB BACK TO 13000 FT. THE CTLR MUST HAVE EITHER KNOWN ALREADY OR ASSESSED THE SIT AND TOLD US TO MAINTAIN 10000 FT. HE THEN SAID 'EVERYTHING IS ALRIGHT FOR ME WITH NO FURTHER PROBS; IS EVERYTHING OK FOR YOU?' I RPTED 'YES; WE ARE OK' AND THANKED HIM. AFTER SEVERAL DAYS; I AM STILL NOT CERTAIN WHAT HAPPENED BECAUSE I WAS NOT FLYING. I THINK RMG WAS MISTAKEN FOR ERLIN AND THE DSCNT BEGAN (AT THE WRONG INTXN). THIS WAS MY 4TH DAY ON DUTY AND FATIGUE PROBABLY WAS A FACTOR. LOOKING BACK; THERE CANNOT BE ENOUGH ATTN TO DETAIL.