I'm sorry, m3vuv, that this is all a bit frustrating, but some parts of this aren't well thought up.
You're talking about a project where (apparently) most of the parts are off board.
What is this MOSFET that you're feeding? Where is it getting power? Why isn't it on the schematic? Why isn't it on the board too?
Why isn't the pot on the board? What are the physical requirements?
You've got the pot going between VCC and pin 7. When it's turned up all the way, it's a dead short.
The discharge transistor on pin 7 will not like that at all (but might not actually blow up).
You need another resistor in series with the pot to increase minimum resistance.
Not only that, it will keep the maximum tick rate from going through the roof.
You're using an electrolytic capacitor for the timing element?
A garden variety electrolytic cap might be +80/-20% tolerance.
You don't have a lot of range on your pot to adjust for such a variance and still cover your 60-180 BPM.
Also, that capacitor is going to age too.
Especially if you are going to build 100 of these, you really have to consider minimizing off-board connections, hand wiring and getting uniform results out of them all.
It's probably not what you want to hear, but maybe a little microprocessor would be easier to do such that 100 of them all work at the same rate without any calibration.
Another trick that was done in the old days was to run the oscillator at a higher frequency, then use a divider.
This allows you to use smaller, precision capacitors.