Keep doing what you're doing.
Maybe you put on some muscle which weighs more than fat so if you're the same weight/size that is still quite a good start.
You built up some muscle which helps your metabolism and now you're starting HIIT cardio, sounds perfect to me.
Watch what you eat, of course, whole foods, no processed carbs or sugars. Lots of fruit, veggies, and proteins, some whole grains.
Keep going, you gotta give it time, is all.