(Accidentally) brewing a partial batch

After successfully making my first batch of homebrew (an Extra Pale Ale from NB), last weekend I embarked on my second adventure: a Honey Kolsch. Unfortunately, I forgot to "top off" the wort with water to bring it up to five gallons before adding my yeast, so now I have a partial batch. I knew something was up when I took the hydrometer reading, but it didn't dawn on me until later.

I plan on doing a secondary fermentation after a couple of weeks in the primary. Can I just boil some water and (after allowing it to cool) put it in the secondary before transferring the beer from the primary, or should I just leave it alone? Are there any other options? Thanks in advance.

i recommend just leaving it alone and enjoy your higher ABV.

Seconded. Leave it alone.
How short of 5 gallons are you?

I'm probably between .5-1 gallon short. I was making this in part for my mom, who usually drinks lower ABV beers. She is the main reason I'd like to add the missing water; I certainly don't mind the extra kick.