I receive SSI and SSA for myself, so I don't file a tax return, so do I need to fill anything out, will my stimulas be direct deposited onto my direct Express card.

The IRS will use the same way to send your stimulus payment as is used to send your SSI and SSA payment.  There is nothing to fill out. 

No, you do not need to do anything to receive the stimulus payment.

See this US Treasury website - https://home.treasury.gov/news/press-releases/sm967

OK by me filling out a return and it getting rejected will that effect getting my stimulas payment went I was supposed to?