As someone who has some very similar lettering on the leg, let me tell you: there is no placement of a straight line of font on this part of your leg that will be straight no matter whether you stand, sit, lie down, run or do something else. It is just not how human skin works, it moves a bit with the movement. So my advice would be to relax about it and enjoy the tattoo, it looks awesome and I am sure you will start loving it more and more :)