CRA needs Schedule 11 and S11, but the summary only includes S11 with watermarks saying "duplicate - do not send by mail". Where do I find the proper forms to send?

can I get rid of the watermark?

No.  The watermark will stay.  CRA doesn't mind about the watermark.  You need to print a full copy of your return if you have not done so to get all of the schedules.

Print the whole return for your records.  Both schedules will be printed out.  There is no permanent storage online, so printing is a good idea anyway.  The watermark isn't a problem.