555 ticks at different frequency than calculated
No you're not doing something wrong, you're just pushing the 555 near it's limits so the non-idealities are getting more pronounced. If you would use 10x higher resistor values I bet that the frequency you get would better match the calculated value.

By using 1 kohm and 2.38 kohm the internal resistance of the discharge transistor probably also starts playing a role. This internal resistance adds to the resistor you used so you get a slightly higher value and a lower frequency.

I suggest that you try increasing the values of the resistors by a factor 2, 5 or even 10 and at the same time decrease the value of the capacitor by the same factor. So for example 5 kohm (instead of 1 kohm), 12 kohm (instead of 2.38 kohm) and 200 pF (instead of 1 nF).

If that still does not give you the right frequency, just change the values of the components slighly. The 555 timer concept is not so precise and certainly not at the frequency you want. In practice, you get something and then tweak it to the value you want.