As everyone says, don't fret over it, and a little above zero.
If you are really worried about it ... some people are that way ... you can take it to a machine shop and have them (re-)calibrate it, it's a simple job, won't cost much. Were it me, I'd wait a couple of years and do it then, though.
Worst thing you can do is drop it. (Even then you are probably OK, depending, but not for certain). Keep in in the case when not in use.