If CRA does not have all of your RRSP Contributions on their system yet, you can manually enter any slips that you have received. It's quite common for this to happen as RRSP Contribution Slips do not have to be issued until May 1st.
If you are NetFiling your return, you do not need to submit these slips with your return but will need them if CRA requests them. If you are paper filing your return and sending it in by mail, the RRSP Contribution slips must be included with the return.
