Knobs in the kit

it’s very hard to put the knobs on the potis. is it normal and the knobs are have the right size for the potentiometer?
i change it, because i was afraid to damage the potentiometer.

It is normal, and you won’t damage the potentiometer.

If you soldered the Lugs to the Pots correctly you can even pull the knob off without damaging anything. Its because the Axis of the Pot is decoupled from the wipers, the load will only affect the plastic housing (when pushed) or the metal bracket around the plastic housing (when pulled) of the Pot.