yes awful system and similar issues. I *think* but still not entirely sure there are 2 places you can login and it is not entirely clear. I gave up trying to follow the links on gov.uk (I mean how effing difficult is it to just let someone login?) and used google which seemed to find the right place.
If I recall, you have to have a government gateway account and wait for UTR, then you have to add a ‘service’ of self assessment. Then you have to wait for the activation code in the post. Then you have to login to gateway enter the activation code, and then you can go to the hrmc site and do your self assessment.
Mine showed as me owing tax (under £500) and said I’d be contacted by HMRC in 72hours, though I’m not confident I understood it right and whether I need to just pay it or not.
People who designed the user experience should be shot.