Sounds like you’re trying to shift passive vocabulary into active vocabulary which will take a bit of doing. @Raionus’ advice is good - the only way you’re going to improve at speaking is by practicing speaking. If you’re not already strong at listening, you’ll need to work on that too, again through conversation or practice via consuming media because speaking and listening are different skills that will both need work.
Depending on what exactly this meetup will consist of and how good the other people will be at understanding you, you may consider prioritizing developing listening over speaking. Making sure that at least one of you can understand the other will probably go a long way towards keeping everything running smoothly. I wouldn’t worry too much about grammar right now. If you have the basics you’ll probably be fine as your friends will probably take pains to speak to you in simple Japanese.

… would be your 
