should the op for "aa" be
+++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++..

and "aba" be
+++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++.>+++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++.<.

no. Output of "aba" don't use two cells. You should use one.
after you output 'a' do next:
+.-.
to output 'b' and return back to 'a'. Your task is to minimalize output length