Note that you also have the dimensions of the input images backwards. They are m x 64 x 64 x 3, where m is the number of samples. You then need to “flatten” them into vectors of length 12288. The dimensions end up as 12288 x m. How you implement that step is critical and is explained on this thread.
That having been said, I don’t think that’s really the problem you are encountering in the later cells. I think your problem is that you have somehow gotten stuck on some incorrect ideas. I think you need to first clear your mind a bit. Go for a walk or get something to eat. Then come back and just sit down and read all the instructions in the notebook from the beginning with a “clear mind”. Then hopefully things will become more clear.
If you still have problems after that, please clearly state which section you are working on and then show us that actual output that you are getting from the failed test, including any exception traces.