Technical Three speed problem

Hi all,
I was looking for an answer, but could not find it, so here is the stupid thing which happened to me.
I am building an AV8 Roadster actually.
When I mounted my floor, I was sticking the shifter into the transmission again. But as it looks in a wrong way. The gears are no mire changeable now. I tried different positions, but it does nor move out of the gear. It was easy to change before.
Which mistake did I do and are there any suggestions to solve this problem without opening the transmission or dis***emble the shift tower? Thank you for any help

 

Make sure the shift forks are in the proper grooves in the sliding syncros.