I agree its a "tad" big, but I have also made this mistake, sometimes its hard to eyeball it right off the bat, and you are sweating. And most of the time you dont want to err on the side of caution (well, at least not too much) because you don't want to "Starve" the snake. I would feed it a much smaller rat next feeding, and maybe step it back up just a little. I only reccomend the smaller rat to make it easier on the jaws assuming you feed weekly.

Ps. Snakes can survive off VERY little food, but lets face it we want our snakes a little fatter than some wild ones