If you pre-ordered last week you should have gotten an email with your registration info. In that case the game should be in Impulse, as long as you click the blue button and set it to show pre-release versions .

If you didn't get the email and don't see it in Impulse, DoomBringer90 speaks truth. support@stardock.com can sort it out.

It said the beta was still open yesterday, but I didn't get around to ordering until today. Then I noticed it was closed, so I'm guessing I have to wait until the next phase. But if you ordered last week, you should be OK.