How many points does priming sugar add?

I made a couple of mistakes as I prepared to bottle my most recent batch.

First, I neglected to take a hydrometer reading before adding priming sugar. My target FG was 1.017 but I hit 1.020 with the sugar. How much of this variance can be attributed to the corn sugar?

Second, I overestimated how much beer I had and am worried I over primed. I added 4 oz thinking I had 4.75 gallons but I really had about 4. Could this, combined with the potentially stalled fermentation, result in bottle bombs?

On the positive side, the beer tasted good.

Sugar will add about 46 points per pound per 1 gallon. You added a quarter pound to four gallons, so 1/16th of that, or a bit under 3 points for your batch.

So there's your 3 points, and I wouldn't be concerned about bottle grenades...

Cheers!

Thank you for teaching me something! And putting my mind at ease.