I'm going to book a flight without agreeing on said date with my friends
Do your friends expect you to go on this trip with them?
Yes, I'm not sure if I can go with them because I still don't have enough money.
I understand you are planning a trip, but you shouldn't book the flight without setting a date with your friends. You may have to cancel your flight if your friends can't go at that time. The tickets might not be refundable.
Are you saying I'm being selfish? I'm surprised you don't care if I go home.
It is rude to book a flight unless they told you to pick a random date. People might not be able to get out of work in time or find a hotel to sleep at.