
If it’s been a few days it isn’t gained fat, it would be really really hard to gain 3 lbs of fat in a few days. It’s probably water retention. When I do intense workouts I often gain temporary weight for a day or two. Muscle recovery often causes weight gain especially if you pushed yourself or if you haven’t worked out in a while because they are holding temporary inflammation to be able to recover and build back up. It will go away soon enough and you will come back leaner if you keep at it.