Declining an invitation does not mean you are not eligible for future consideration in a round. It does mean the profile is submitted back into the pool. If you fail to complete the invitation in the 60 days, your profile will be eliminated from the pool. Any future consideration for permanent resident status in Canada means starting the process over from the beginning.
If you are not invited to apply in the round or in any round within a year (12 months) of the date of providing your profile, it is removed from the system. The profile expires, but interested individuals can start the process again by completing the profile step and going back into a pool after the 12 month time.
It is important not to create more than one profile. Individuals with a profile in the pool can withdraw or delete their existing profile by signing into their account and clicking on the application and the withdraw profile button. Once it has been withdrawn from the system, a new profile can be created.