You have to go into the Collection area (press U) and click the mounts tab at the side, then right click on the Imperial Horse and select it as active. Then you will already have your horse (just press H), you will not need to select it from the stable.
Thanks Hook. I also noticed on those tabs any race/any alliance from my pre-order is listed as purchased in the crown store I guess they prob will be opening it up.
"There is only one god, and his name is Death. And there is only one thing we say to Death: Not today." -Syrio Forel
Your welcome, and the Crown Store will open on Monday. There will be a stress test event at 6PM EST where everyone gets free crowns to spend as fast as you can to try and break the store!