Your system (pressure switch setting) will give you a variation of 30 to 50 psi. You can reduce that effect by increasing the pressure settings to 40 to 60 psi. There is usually a nut in the top of the pressure switch that you can turn clockwise to increase both the cutin and cutout pressures together.
You may have a problem with the air in the pressure tank. Most tanks are "bladder tanks" that have a rubber bladder or diaphragm that separates the air from the water. Following is the procedure for checking the tank. I suggest you do this BEFORE you adjust the switch.
0. Open a valve until the pump starts and immediately close the valve when it starts. Measure the time (seconds) from pump-on to pump-off. If it is very short time, you need more air in the tank and may have a failed bladder
1. Find an air valve somewhere on the tank. It should look like the valve on your tire. Get your tire gauge.
2. Turn off the power to the pump.
3. Open a water line and drain water until it stops coming out of the faucet. A place near the tank is easiest to work with.
4. Close the valve when the water stops running.
5. Measure the air pressure at the air valve in the tank. It should be around 28 psi (2 psi less than your 30 psi cutin pressure).
6. If the pressure exceeds 28 psi, bleed air to 28 psi or increase your switch setting to start at 2 psi above the measured pressure (but not over 40 psi).
7. If the pressure is below 28 psi, increase pressure to 28 psi. If it was much lower than 28 psi you may have a failed bladder, which we will discover later.
8. Turn on your pump and see if it shuts off as expected. Check the time (seconds) from pump-on to pump-off.
9. Operate your system and see if performance is acceptable. If the problem returns, repeat steps 3 to 5. If the pressure is now significantly lower than 28 psi, you probably have a failed bladder or tank. Replace the tank.
If you want to operate the system at higher pressure, see the first paragraph.