The answer is pretty simple: apply thin layers, and allow enough time for each layer to cure under the light. The pros had a few other tips for preventing bubbles, as well.
"Before applying gel, NEVER shake the bottle and start applying," Edwards said. "Always roll between your hands and begin application." She also warned not to leave the gel bottle too close to the UV/LED lamp. "This alters the gel and can create a partial cure before you place on the nail."
Elle reminded me that prep is key. When I mentioned my theory that the shower had warped the polish, she said, "It's not after a gel manicure that you have to worry about water, it's before. The nails need to be dehydrated and lint-, oil-, and lotion-free. Always swipe nails with a lint-free wipe using an alcohol-based prep before application of gel . . . If any oils or lint were on the 'inhibition layer' (sticky layer that is left after cure), this can cause the gaps in the gels and improper adhesion between layers."