The error message indicates that the error is generated by this line:
bottomTtest=ncread(fullfile(fp,'Temp_Q1(2020).nc'),'bottomT',[1 1 1],[length(lon) length(lat) 1 1]);
The error is due to the fact that you've specified 3 start values but 4 count values
bottomTtest=ncread(fullfile(fp,'Temp_Q1(2020).nc'),'bottomT',[1 1 1],[length(lon) length(lat) 1 1]);
% ^^^^^^^ 3 starts
% ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4 counts
just like the error message says: "COUNT has incorrect number of elements (4). The variable has 3 dimensions."