Fat girl here😜

Seriously I know I'm fat and I know I need to lose a lot of weight it effects my fiancé, my family, my job and myself. 5'3" 273lbs my fiancé and I want kids and I know me being this weight effects my chances of getting pregnant and having a life that a more fit person would have. I hired a personal trainer and I joined the gym but I know what really needs to change is what I eat. I eat fast food way too much because it's easy and quick but I don't really know how to cook anything that is healthy and good to eat. So I struggle Day to day on what I should eat with my schedule and how many times I should eat and this and that... in all I'm not really good at this and I get overwhelmed when I think about how to start and how to start because I don't want to make a mistake and mess it up and gain even more weight. Kinda what my biggest fear is not actually knowing what I will look like when I lose this weight. I'm really afraid of getting saggy skin because I am 22 years old.