Omg- this happened to me on my 3 tier cake this weekend. I to am new at this and its my first big cake order. A Topsy turvy and I did everything you did. I know for a fact that the your cake was slammed. Why? Because my husband and I transported my cake on a flat surface. Cake was fine when we arrived to the location. It was when he took it out of the car and started walking about 20 steps and the cake slid -I think he held it in an angle it slammed towards his chest and to the box. It was the front of the cake
I then proceeded to try to fixit. It was fine but when we had to move it again and he placed it on the table I noticed the area where thecake slid and slammed it cracked. Then minutes later that large piece fell!!! I wanted to die.. I stayed calm worked fast took the icing and pasted some to the back of the piece and placed it back and started my touch up. I to used the 1/2 inch board which I felt alter we delivered could of been stronger. FYI - the cake print from the slam is still on the cardboardnox. I think if the cake had not hit that cardboard so hard it would of been okay. So sad, your cake was beautiful.. I have not slept well since Saturday and I am still feeling lousy about it. I will post mine later today to share.