That does seem high, although the sedentary MFP setting and your gender and size mitigate that somewhat. (A petite woman with MFP set to very active would have a much harder time legitimately getting that sort of adjustment.) Which Fitbit do you have? If you have an HR model, then you might look at your heart rate and see how it correlates with your steps and known activity. Does it seem reasonable? I know that sometimes I've had my Charge HR in my hand or my pocket - so it can't have been getting good HR readings - and it has shown a high heart rate. I think the device has trouble distinguishing between a bad signal and an elevated heart rate. I now try to be careful to turn off the HR function before I take it off and carry it for any length of time.

Adjustments are the difference between your Fitbit burn (TDEE) and your MFP activity level. Enable negative calorie adjustments and increase your activity level.

Then trust your Fitbit for several weeks, reevaluate your progress, and adjust accordingly.

Weight loss is not linear! Read the Sexypants post: http://community.myfitnesspal.com/en/discussion/1080242/a-guide-to-get-you-started-on-your-path-to-sexypants/p1

Well, 7.5 hours in the fat burn zone is a lot, so I suspect that explains why the big adjustment. I suspect the biggest question is whether your heart rate was up because you were truly burning extra calories or if it was up due to other factors (excitement, etc.). For instance, I haven't ridden a roller coaster in years but I would imagine that I'd show an elevated heart rate, and thus, an elevated calorie burn on a good one, even though I didn't actually burn those calories. On the other hand, since this was probably a one-time sort of thing (I assume you don't go to big street fairs every day), it doesn't matter that much if it was accurate. If it is an every day sort of thing, then you need to track it down.

Based purely on your number of steps, your adjustment seems high. Based on your heart rate, it might not be. You say it says you climbed 26 floors. That doesn't affect your calorie count, but if you really did do that much climbing - of hills or stairs - then that argues more for accuracy, but don't trust the floor count. It's notoriously inaccurate. I can get 100 flights of stairs just walking around inside my house on a windy day.

Over the short term, if the adjustment was accurate, then you're good and that 3 pounds is water weight. If the adjustment was high, then you overate.