what is wrong with my leaf??? i have picture...

you overwatered and the plants leafs drooped into the wet soil. when it sprung back up it had water on it which magnified the lights intensity causing a slight burn. nothing to worry about just watch how much you water and make sure your pot has good drainage!

if it's in a fertilized soil, it could be nute burn

it is also very young. young plants will show things like that b/c of genetic defects. yes it could be a number of other things. but if you start making adjustments and going ape shit about the very small brown tip right now, then you could just as easily mess it up worse. in general, that plant looks good. chill out, smoke a bowl, and let it get growing a bit first. if it gets noticeably worse in the next week or so then let us know. it's really just too young to make any diagnoses at this point and there are too many variables, unless you were growing in a COMPLETELY controlled environment, which you aren't.

I second leaving it alone, it looks like it was caused physically, not internally.

lol you guys are wrong. its from being overwatered. look at it, its in a cup... ill bet the holes he has in it to drain are tiny if he has any at all. and fertilizer doesnt matter as long as hes not feeding it his own nutes. i use miracle grow time slow release soil for my seedlings and they dont get that. look at the tip, its brown from being dried out. thus is dropped into the wet soil and came back up and burned. it is not too early to tell whats wrong.