Think both are accepted spellings- https://www.google.co.uk/search?source=ig&hl=en&rlz=1R2GGIE_en&q=rigmarole+meaning&oq=rigamarole&aq=1s&aqi=g-s10&aql=&gs_l=igoogle.1.1.0i10l10.969.3781.0.7687.10.7.0.0.0.0.594.2235.0j1j4j0j1j1.7.0...0.0.
but in this case the 10 letter one may be correct, although Chambers gives "rigmarole".