Is the drum filling up with line before the jib is all the way in? How much line is on the drum to start? Can you use a smaller diameter line?

And of course this "Duh" question... are the sheets loose when you are furling? (rather than actually loose, I tend to put just a touch of tension on my sheets so that the sail furls fairly tight... but the sheets have to be loose enough for the sail to want to roll up.)

Usually I find that just getting the furl started is the most "difficult" part... once the rollup starts, it works well... so your issue of difficulty at the end of the furl is a different beast altogether.