I literally can’t stick to a deficit for the life in me

Okay so I’m genuinely having a moment over this because it’s literally killing off, so I’m about 166cm ish and about 53.5kg ish and trying to drop back down to somewhere in the ballpark of 50 before Christmas since that was what I was maintaining at for about a year. I’m trying to eat about 1300 cals but i literally can’t stick to it, and I know that I can given that I have lost weight before in the past, but I always just end up eating half of the fridge when I get home from sixth form, which isn’t particularly pleasant in the aftermath. I either go to the gym every day in a week or go like twice so it’s kind of hard to work out my maintenance when I’m super inconsistent because of school 🙈. Any advice on how to stick to a deficit would be appreciated thank you :)