Should I dilute or not dilute my wort?

The ingredients of your recipe are written in proportions for a 5-gallon batch, so if you don't add water after the boil to get to that level, then you'll have a concentrated beer that is higher in alcohol. It's difficult to predict the effect on the taste, but it could be a tasty imperial version of your beer. Just the opposite happens if you put in too much water...... you'll have a watery beer that is lower in alcohol.

It's normal to brew the 3-4 gallons of liquid like you did and then add some top-off water. I do this and use my water to help cool the wort quickly before pitching the yeast. The top-off water is boiled and then cooled by some brewers to add extra sanitation, and some will use straight tap water (or bottled water). Whichever you choose may depend mostly on how much chlorine is in your water. You need to get rid of it.

 

In general terms, you beer will be proportionally stronger or weaker if you deviate from the intended volume. For instance, if the intended recipe is for 5 gallons and you leave it with with 4 gallons your beer will have about 25% higher starting gravity and therefore about 25% more alcohol in the finished beer. This is not necessarily an issue, it will still be beer, but the recipe was likely developed with a certain balance between ABV, IBU, etc, and you will be changing that intended balance.

 

Beat me to it.