Shorted water amount

After brewing the Bavarian Hefeweizen, I thought I brought the total liquid to 5 gallons in the primary fermenter. That was 1 week ago. I went to transfer to a 5 gallon carboy and noticed on the primary that I only brought the brew up to 4 gallons.

Can I add the 1 gallon I am short for the last week of brewing or leave it as is?
Or have I ruined the batch?

Thanks

I would not add water post fermentation. you did not ruin a batch, it will just be stronger with more alcohol (assuming you fermented 4 gallons instead of 5)

Before you brew your next beer find a way to measure out 5 gallons accurately and then do it and mark you primary. Old milk jug, measuring cup, whatever. Do this and then you always will know.

You haven’t necessarily ruined you batch but it may be more concentrated than you anticipated right now. I’d say just leave it. Did you take gravity readings?

I’m new to this so keep that in mind. On my very first brew I shorted the batch by a gallon. I boiled a gallon, chilled it and added it to make five gallons. To me, it came out fine.