first of all, 1200 kcal/day is way too low for a big guy like you, you won't have an optimal amount of micro and macronutrients, you absolutely need enough fats in your diet for optimal hormonal health, carbohydrates for weightlifting and college performance and protein goes without saying
even then, i highly doubt that you would be able to sustain that low amount of calories if you tried, without tracking calories you would most likely underestimate what you eat and as a result severely overeat
next, in my opinion walking is not a legitimate form of cardio
my advice is:
make yourself a meal plan with optimal amount of protein, fats and carbohydrates with a deficit of 20-30% of your current maintenance level calories and stick to eat
track what you eat daily and weight yourself every week on the empty stomach in the morning to see if you are loosing weight, if you hit a plateau - adjust your diet plan accordingly
don't rely on walking, start doing an actual cardio: it can be jogging, biking, rowing, etc (there is a plenty of machines in the gym to choose from)
do weight training as muscles will make you burn a bit more fat passively + will make you look leaner, but prioritize cardio
do your homework, research, try things out and keep your mind open, find what works best on you and don't blindly follow other peoples advices, my own included
and if you struggle, come here for support and motivation
