Well, don't say that. That's my first tip.
No one has a thing they say after they make out. Your problem is not that you don't know what to say, but that you feel so awkward and think you have to say something particularly special.
Basically, if you feel awkward, and you're giving into that feeling, anything you say is going to sound wierd.
Challenge yourself not to feel awkward and be totally calm afterwards. What goes on in your head and stops you from feeling good and calm afterwards (or stops you from feeling excited and wanting sex). That is the real issue. Post again when you've confronted this.