I think I'm Shifting Wrong

1st gear accelerate to 4000 RPMs should be about 20 mph and push in the clutch. Shift to 2nd gear and release the clutch pedal as the RPMs drop to ~2800 (release steadily, not necessarily slowly, but not dumping it either).

2nd gear accelerate to 4000 RPMs should be about 35 mph and push in the clutch. Shift to 3rd gear and release the clutch pedal as the RPMs drop to about ~2500.

If you change the 4000 RPM shift to 3000 RPMs then the engine RPMs will drop to ~2400 and ~1900 for 2nd and 3rd gears, respectively. Watch the tach needle when you release the clutch and see if it jerks slightly up or down before settling at the engine's desired RPM - if you see this or you hear the engine rev itself those are indications that you missed the butter zone for the shift (this is easier to see when the RPMs drop below the ideal mark)

Note that all pedals should be operated smoothly without mashing on them or dumping them. My recommendation if you can't get to a track is find a large enough empty parking lot and practice these shifts (include 4th too if you have room)