... OK, so it looks like the recipe assumed a Brewhouse Efficiency (BE) of 75% ... and depending on whether you measured that gravity of 1.032 at 18.8 lts or after topping up (to 21 lts? and after giving the wort a thoroughly good mixing with that water?) it looks like you've achieved a BE of around 50-55% ... Ouch! ... of course, if you measured that gravity after topping up, but you didn't mix that water in thoroughly, then this may be a case of the issue some kit brewers have with measuring a gravity where all the sugars were sitting in the more dense wort at the bottom of the FV5.5 US Gallons, so about 21L.
1) I started with 23L in the Peco boiler for a 60 minute mash. That was a pure guess.
2) I then topped it up once I took the grain out and set the Peco to boil for 60 mins. Boiling in a Peco is done with a loose lid. As opposed to a converted cooler or an enclosed system, this does increase the boil off.
3) Before I screwed it up by adding more water to the FV, I had about 18.8L in the FV
If you're sure you mixed thoroughly ... follow what Terry said