this could be a number of things,
iam guessing you have bots playing aswell when u test yopur map, and only have one playerstart in the map , so yoursel and all the bots telefrag each other once the game starts, solution is to add more player starts or specify the number of bots that play, an make sure u have enough player starts for each bot
secondly you could have a terrian in your map and you accidently raised the terrian over your playerstart without even knowing.
what i would do is select all playerstarts an delete the lot of them then just add one again or more if u wanna play with bots rebuild then try again,
this should sort things out