Basically I've been making plans for my birthday which is in beginning of May making plans with different groups of friends but for one particular date I haven't had a response from some of the group do I wait or ask my other friends if they want to do that date? I'm just worried about leaving until last minute it won't happen
'Night out' - this is what I meant about being monosyllabic. You have been nicely asked by a poster who is always pleasant and supportive of you about what you are doing to celebrate your birthday with some examples and you just answer 'night out'. That's almost a given.
What have you invited your friends that haven't responded to do? Is it something they may have to think about?
If you're only worried about one person then stop worrying and just plan with the others who have responded. It's the coronation weekend so you'd be better getting on with it and what you're doing as lots of places might be busy with events.