My extract/partial grain kit calls for a OG of 1.057 - 1.061. After topping off in the fermentor, my OG was 1.074. Is this close enough? Did the addition of water raise the OG?
Adding water to something will lower its gravity.
When adding water to wort from a concentrated extract brew process its not uncommon for the two to not mix completely. When you added the water you turned over some of the wort and took a sample of something that was more dense than intended. No big deal. It will equilibrate and the fermentation action of the yeast will stir it up once it gets going too.
Next time, add your top up water and either stir with a sanitized spoon or seal the fermentor and shake it. Then take your sample for gravity readings.
Happens to everyone at this stage in the hobby.
Adding water post boil will dilute and lower the OG, not raise it.
It's possible your readings were off.
Hydrometer If using a hydrometer make sure the wort is cool and follow the temp correction values for your hydrometer.
Refractometer Make sure your refractometer is zeroed out using distilled water.
1.074 is the ball park low end gravity for many "big" beers. The added sugars require more yeast for fermentation. Double check your readings and pitch accordingly. If you do it right, the only down side of higher OG is more alcohol, if done wrong you may get an underattenuated beer that is sweet.