Advice on saying no

So usually when a situation involves men I'm very good at standing up for myself, but a week ago I was with this guy and he ended up pressuring me into going farther than I wanted. I realize I shouldn't feel bad about myself, but it kind of dinged my confidence a bit and made me feel slutty. Throughout the entire time he would keep asking me why I didn't want to go farther and telling me that I couldn't just leave him like that. So, I wanted to get everyone's advice on how I can be stronger if there is a situation like that again. Thanks everyone 💙