This your problem:
Can I count part-time work toward the work experience requirement?
You can count part-time work toward the work experience requirement, as long as you were not a full-time student at the time.
However, you must have gained the equivalent amount of experience as someone who worked full-time for at least one year (1560 hours
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=393&top=29
You were studying full time during May 2011 to June 2012. Simultaneously, you were working full time. As per the above FAQ, this full time work experience cannot be counted towards your work.