What should I do?

Hi y’all

My ex broke up to me a week ago. And we’re seeing each other on this friday on our mutual friends birthday party. I also heard that she met someone new. Any advice how I should act in this party around her? Also she said that she wanted to stay friends and what if she comes chatting to me, me knowing that she found somone else that quickly. I want to say that when we broke up I begged and acted needy and I regret it. It made me look weak. Few days after break up she asked how my family member is. Cus I told her that someone close to me got into hospital. So asked whats the situation and after few hours I replied that its all good and nothing else. We havent talked with each other since. Any hope that she starts to realise what she lost and starts to miss me? And how I should act on friday in that birthday party I talked about? I have no problem stopping myself from calling her or texting her, so no contact via online is easy at the moment.