(2) It is unfair, because the probability of Xiao Zhang getting 3 points is 0, while the probability of Xiao Li getting 3 points is 0.

Changing the second 4 to an arbitrary odd number, such as 7, will make the game fair.

(3) If Xiaojun enters the maze center x times, then (10-x) does not enter the maze center, then the sum of the total scores of Xiao Zhang and Xiao Li is 2x+3( 10-x).

According to the meaning of the question:

2x+3( 10-x)≤28，

The solution is x≥2,

Therefore, Xiaojun entered the center of the maze at least twice.