that is a fricking small range. Do note a lot of servo's have some hysteresis so don't expect exact results on that small range.
Some hints/qurestions:
- Edit you post to include code tags! See How to use the forum. While you're there, read the rest as well.
- Do you know why we like to use variables?
- Do you have pull down resistors connected?
- DON'T power the servo from the Arduino directly. Get a proper supply for it, servo's are hungry beasts
- Use state change detection to see if the button became pressed (which is not the same as is pressed
- If you want easy, grab a library like Bounce2.