I think one of the best ways to stop yourself speeding up if you're nervous is to use a metronome.
If you're presenting without a laptop search for a vibrating metronome on your app/play store. Set it to 60 bpm then you can just rest your hand on your pocket and get a grasp for how quick time is going. Or, if you decide you want to speak at around 140 words per minute (which is in the recommended conversational range), you could set it at 140 or a factor of (say half, 70) and use that to check yourself.
I'm sure there's similar apps/websites you could use on a laptop as well, or just open the clock and note how quickly the seconds are going.