I think you went to the wrong place.
1 - go to the full web address:
http://www.sgrid.com/forum2 - click on "Register" near the top of the screen, all the way to the right.
3 - Fill out the form, and submit it. If you have a Facebook account, you can also connect to it.
4 - Wait for the validation email, open it, click on the link, and you're in.
5 - If you don't get the validation email, leave a note here, and I will log in and manually validate your account. (I just tried, but I can't find any account for "gokemidoro".
I have no idea how you could have registered there for A-Main - unless you clicked on the A-Main logo at the top of the page, which would have taken you to the A-Main website, so maybe what you've just done is sign up with A-Main Hobbies... which is a great place!
I already have an account on RC Universe - will check that out tomorrow; it's now 2am, and I'm getting sleepy. :-)