Will I owe a penalty since I turned 70 1/2 in February 2017, but did not take my RMD until mid-April 2017? If so, how can I request a waiver due to my mistake?

I turned 70 at the end of August 2016, so 70 1/2 near end of February 2017.  Is the RMD required by April 1 of 2017, or by end of 2017?  If it is required by April 1, 2017, and I take it now (mid-April), I would want to request a waiver of the penalty caused by my misunderstanding.  If necessary, how would I go about that?