The first layer is the most important part of your print. if your nozzle is too close it could clog up your hotend, or your extruder will skip steps. If your nozzle is too high your print will not adhere well to the bed and the job will fail. Calibration is key but sometimes things are off and it can be quite frustrating to get it right especially when your in a hurry.
Luckily for you, there is a way get it right quickly and easily.. even after it started printing. its called babystepping and its built into your Marlin Firmware.
If its not turned on, You can enable it in the Arduino IDE once you open up the marlin firmware configuration_adv.h file. do a search for baby and it will show up.. you just need to remove the // before #define BABYSTEPPING and then also change the multipler to 16.
This is what the section of code looks like (Marlin RC6 Bugfix)
// Babystepping enables the user to control the axis in tiny amounts, independently from the normal printing process
// it can e.g. be used to change z-positions in the print startup phase in real-time
// does not respect endstops!
//#define BABYSTEPPING
#if ENABLED(BABYSTEPPING)
#define BABYSTEP_XY //not only z, but also XY in the menu. more clutter, more functions
//not implemented for deltabots!
#define BABYSTEP_INVERT_Z false //true for inverse movements in Z
#define BABYSTEP_MULTIPLICATOR 16 //faster movements
#endif
give it a try, it really made my life easier.
Marlin can be downloaded here.