You are having difficulty attaching the Blossom Controller to the terminal bracket.
For maximum security and weather-proofness, the controller attaches to the bracket quite stiffly -- but it will fit!
Make sure that all the wires coming from the Bracket are in the notched area for access, and not overlapping with where the Controller will attached. Also, make sure that the bracket and Controller are oriented the same way. You can check to see if the connectors are lining up. Once you have taken these steps, push the Controller firmly into place.