Hi Nicole, my guess is that the 2500 would be more accurate than the 1800, unless you're really on the tiny side. Being young, being athletic, and with that much of a workout (cardio and weights), you should be a calorie burning machine. It seems hard to believe you would add a pound of fat in a week. There are a lot of things that can cause weight to fluctuate; maybe water retention for one. Make sure what you eat is healthy (fruits, veggies, lean protein, healthy fats) and you should be good. Keep an eye on it for another week and see what happens, would be my first thought.
And now that you don't have to be perfect, you can be good.