Hard to tell from your picture, but the spherical shaped side of the nut goes against the lever arm.  Then the jamb nut goes on last.

You can place a 1” long tube 3/8” ID over the threads if you need more adjustment.  Between lever arm and adjusting nut.  Grind the end of that tube rounded where it indexes against the lever.

Yours is unusual.  Usually the nut will only have a few threads showing at the end of the adjusting threads.
If pedal is hard, you either have too stiff a pressure plate ( like the one in my 66☹️) or the throwout bearing is hanging up on the bearing retainer sleeve of the tranny.  Did you check that the bearing slides easily on the tube before putting it together?  Was it lubricated?  There is a void in the bearing dlide that needs to be packed with grease.   A bearing retainer tube that is worn can cause near impossible clutch operation if the bearing catches on a groove.

Also, since you have so little adjustment, you might want to lengthen the pivot stud in the bellhousing to correct that issue.

Be sure throwout bearing is correct one for cable clutch linkage and that it is properly attached to the lever arm.

You do not want any bends in the cable other than the one around the oil filter.

Check to be sure the hole where the cable goes through the firewall is not rubbing the cable.