ImmCanada, help needed. Thanks

I have a question regarding the occupation definition. I have three years of
work experience as an engineer and 4 years of experience as a research
assistant. And currently I am still a research assistant. So my occupation
history will have two NOC codes. And which one should I use for application.
Will there be any contradiction if I list both of them in my career history?
Does the #13 of the application form have to be the same as your desired
occupation you want to use for immigration?
Thank you