Nice work, it's a fun movement mechanic and the game is insanely polished. Only last minute tweaks I would consider are a few flow type things. You could reduce the amount of time you show the "Space Juice" logo, and tighten up the in-between timings when you restart a level. Seconds are precious here, especially if someone is flowing with the game. The delays are friction points. In that vein, when completing a level, you might just want to give a "next level" button, instead of having to go out and to the home screen, select the level, etc... Again, it's small, but if someone is in the flow, protect that.
Another small thing to consider, is helping to indicate what is happening when you leave the "bubbles". It feels like the controls just lock up, which isn't great. But now I see that it's because there is no atmosphere, the rudder mentioned does not work. If the little "trail" would still whip back and forth as you steer, that might help. But then again, it might create other frustrations. All you need, really, is something to happen when the user hits left/right, visually, so that they know their controls aren't locked. Perhaps even allow just a really small amount of turn outside of the bubbles. That would both message what is happening better, and also potentially create some really fun and tense moments when a player is juuuuust able to get back in.
Great work, and good luck on the launch.