Advice on Flattening Belly and Caloric Intake After Weight Loss?

Hey guys, I am 19F, 57 kg (~125 lbs), 173 cm (5‘8‘‘) and despite being pretty close to being underweight, I still have a pretty big belly. I have read some fairly contradicting things on the topic of flattening it (namely that, on one hand, I should focus on a caloric deficit, on the other hand, I should build muscle which needs a surplus) so I figured I'd ask here for some guidance ^^'

For context:

• I've been on a caloric deficit (1500kcal/day) for the past year which helped me lose about 18kg (~40 lbs), and I only recently (about 2-3 months ago) switched to something between maintenance and deficit (1500-2000kcal/day).
• I've also switched from hitting the gym for 4 pilates/yoga classes a week to 2 pilates classes + 2 glute-focused strength training sessions + 2 upper body strength training sessions and eat about 110g of protein. (This change has been inspired by the fact that I also want to work on my glutes as I have neglected them during my weight loss journey...)

Does this seem like a solid plan? I’m especially unsure about my caloric intake to meet both my goals (a flatter stomach and a bit more developped glutes). Should I keep it at maintenance? Or go for a slight deficit? Surplus? (I have to admit that going into a surplus does make me quite anxious after a year of being in a deficit.)

Any tips or reassurance would be super appreciated!