Will I gain weight if I eat around 1000 kcal everyday but eat 2500+ once a week?

I want to maintain and I eat very healthy, mostly veggies and fruits, very low carb and no sugar almost all week and no more than 1200 kcal , go to the gym 4 times a week and walk a lot but once a week I will go over my calorie limit, sometimes more sometimes less and it’s honestly mostly junk and sugar but I’m afraid I’m eating more kcals than I think and will gain weight, it’s this possible?

Will I gain weight if I eat around 1000 kcal everyday but eat 2500+ once a week?