Not Enough Water

I recently made a Hefeweizen from Extract w/Specialty Grains and just realized that I was a half gallon short adding water prior to the primary fermentation. Will this negatively affect the taste of my beer? Also, what would be the effects of adding that half gallon back during my transfer to the secondary fermenter, i.e siphoning the fermented beer on top of the added water? The OG was high and I know this is why.

Leave it be.

At best you are giving yourself 4 more pints of beer.
Taste it when you move it to the secondary and ask youself if it would taste any better with 10% more water.

It is not recommended on adding anything (but fruit/spices) to already brewing beer.

With that said, you can always boil the shortage, cool, and add if you wish, but you may end up contaminating your brew somewhere along the line.

I can't believe I did this personally. I just didn't want to go through the entire process and end up with a terrible product for something I could have corrected somwhere along the line.

Undershooting your target volume (or overshooting) happens way more than you imagine. It's not really an issue.

Thanks all! This makes me feel a little better about my mistake.

IMHO, it's better to undershoot than overshoot.

Tasted this during transfer to secondary last night, FG was really close and other than the expected flatness the brew tasted pretty good. Thanks for talking me off the ledge guys.

More flavor is almost always better. Hell, if budweiser added half the water it might actually taste like something.