Thank you for thoroughly testing the leveling system during this phase of the beta, and continuing to provide your constructive feedback for Heart of the Swarm. If you'd like to participate in the beta, you can gain access by pre-purchasing the game digitally on Battle.net.
I purchased the Heart of the Swarm regular edition, and I don't have beta access. I've already opted in for Starcraft 2. I see an entry for Heart of the Swarm in my games, but when I click to download the client it downloads the regular Starcraft 2 installer, and opens regular Starcraft 2 when I run it.
tldr; How do I access HOTS beta after pre-purchasing HOTS?