Engagement party advice?

So my fiancé and I got engaged last month and we are going to have our engagement party next week. We were going to wait longer but my mom who has breast cancer found out she's having her masectomy at the end of November and she won't be able to do anything after that. So we planned it early so she could come. But planning it early has caused so much stress for me. I invited so many people but only half have RSVP'd and my work is under renovation so I haven't been paid lately, therefore I don't have the money to by the bridesmaid gifts I wanted. I need some advice on making things less stressful and more fun. It's our engagement party, it's a celebration, it shouldn't have to be so stressful. Any advice you guys can give me?