Hustler 6BTV 60m add on kit issues

I’ve been trying to install a 60m add on kit to my Hustler 6BTV vertical antenna.

Unfortunately, tunning it to the 60m band is next to impossible and the antenna’s 40m SWR is quite a way off.

As you can see from the graph I’m a looong way from 60m frequencies.

Any suggestions would be appreciated!