2001 Mazda Protege timing and starting hard

me and my dad changed the timing belt in my car and afterwards it wanted to start really hard. we are wondering if the timing could be off or it could it be something that we have looked over. after car is started it will turn off and on no problem. just the initial start is hard. im at lost for ideas on what it could be. im in need of help. if anyone has had this problem before please let me know what you did and how you fixed it, thanks