Most folks want to know how they can get their tunes UP to session speed. The best solution may actually be to slow them down.
Hitting the right notes on time in a tune does have something to do with remembering the tune... but that's only part of the challenge. Good rhythm also means hitting your notes at the right time, in the right part of the beat, steadily and solidly... and consistently, at a steady tempo throughout the whole tune. At any tempo.
It is not easy and there is no shortcut. There's really only one way to do this: Capture a disciplined bodhran player with perfect rhythm, chain him or her to a pole in your basement, and make him practice with you every day.
Ok, there is another option: Use a metronome.
Find a tune you know well. Set the metronome to a slower tempo than you're accustomed to, then try the tune again, and stay in tempo. You'll find that your fingers want to rush through--especially those nice little runs that fall so nicely under your fingers at tempo. Keep working the tune until you can stay right with the metronome. An intensive exercise in motion control. Think like Tai Chi -- slow, even and steady movements.
Then, do the same with your new tunes. It will take you miles toward excellent finger control and will really drill your knowledge of the tune. In other words, it will kick your heiney. The same thing the bodhran player will do when you set him free, so be careful.