Too much water in coopers draught

[RIP]

I did a second brew the other day, the first being a tom caxton real ale which is conditioning now. The second brew, coopers draught, I added Tesco bottled water until it was at the 25 litre mark on the ferm bucket. Just read the instructions again to see how long to leave it fermenting and realised it says it should be 23 litres, not 25, like the real ale was. The F Bin is chucking out a bit of foam through the airlock and I've had to top up the airlock with water a few times, I presume due to the lack of air space above the liquid. I think this will be OK but will the brew be weak with the extra 2 litres of water?

[Barm]

Clearly the OG will be lower than intended, and the brew correspondingly weaker.
TBH I think most 1-can kits tend to be on the thin side anyway, and ususally shorten the length to 19 or 20L instead of the 23L as per the instructions.
If you're desperate for a particular strength, plopping a hydrometer in the freshly-made wort and then topping up with water to the desired OG is the way to go.

For now: you could add extra fermentables - but it'll need to be spraymalt to build the body back up; adding sugar would contribute alcohol only and still leave the beer thin. The downside of this is that you'll alter the hop balance, reducing the brew's bitterness and hop flavour.

Or just chalk it up to experience - and work your way through 25L of slightly-weaker-than-it-should-have-been-due-to-little-cock-up beer!