Whats the worste that can happen? A slightly crooked tree? In nature a root grows down and chances are it will hit a small rock or shell or the root of another plant and end up bent off to the side,seeing as how its still small I'd say its not a big problem, if the trunk is crooked you can always straighten it with a piece of Cord, three strips of foam and bit of stout stick

mango trees naturally grow all bent and crooked, taproots will correct themselves due to earth's gravity

Thanks for the replies. My mango tree does seem to be doing well. Now I feel better!