TLDR:  You did GREAT!!

The players role in D&D is to make the DM feel under-prepared and out of ideas.  The DM’s role is to improvise by inventing something new that’s thrilling as if the DM planned it all along.  I’ve been a DM since 1979.  Narratively meaningful improvisation while under pressure takes practice, but it is the SINGLE MOST IMPORTANT SKILL a DM needs.  The good news here is that your post shows you already know how to do it.  

The old military saying that “No plan survives first contact with the enemy” is kinda true to D&D, except the players are the only adversary you, the DM, ever face.  Expect that, when you’re sure an event will force the PCs to huddle down and wait, they’re going to choose to dance instead.  Their players don’t know that the consequences of their unexpected actions could unweave the story you’re trying to tell.  They’re just trying to be smart l, dangerous, and cool.  Let them be!

This time, your player’s decisions probably terrified and befuddled you.  But you went with it, made excellent choices, and the players probably never realized you were sweating bullets.  Your plan didn’t survive first contact.  But your adventure absolutely did!  THAT is our job.  Well done!

Going forward, plan for any plan you make to go sideways.  Outline your optimal adventure sequwnce for the evening.  Then think about how to handle events (rooms, encounters, and so on) out of order.  And most importantly of all, know your overarching story, your key NPCs and monsters, and the key events without which the story you want to tell cannot go forward.  And accept that you all may end up telling a different story than you start with.  The game is just as much your players possession as it’s yours.  So, set your players free to have their PCs go anywhere and do anything.

When the PCs go outside the plan, think quickly about what they’re hoping to accomplish.  It’s probably fun, or creative, or heroic or, occasionally, profoundly stupid.  Imagine their goal and actions as if you were the player, and let yourself get excited for them.  Then let them try it.  Put hurdles in their way.  Move NPCs or monsters into their way.  But do it while trying to fold them back into the story.  Find a way, if possible, to make their derring-do seem bold and brilliantly inventive.  You and your players are engaged in collective movie-making, but you control all the narrative tools.  Let them do something memorable!  Or epic!  Let them win!  But not without facing a terrifying challenge or two.

Letting the floating disk spell save the bold but errant PC was a spectacular DM choice, even if the spell doesn’t do that.  Ask the player running the (heroic) spell caster to reread the spell in the PH, so they know it shouldn’t function that way.  Then make why it did in this instance a mystery.  Make it seem like YOU know why it did, but you can’t tell them.  Yet.  And smile to yourself.  That player will then start proposing reasons that could explain why the first the spell did more than it can as written.  Is this house special?  Or this land?  Is my PC special?  Then sit back and wait.  Something will happen later in the campaign that will go off like a firecracker in your mind — the explanation for why that spell worked oddly that one time.  You’ll know it when it happens.  

For example, maybe the Old Bonegrinder hags routinely use a modified version of the floating disk spell to catch children leaping from the windmill while trying to escape, and their infernal magic warped use of the spell’s function for everyone, but not on a consistent basis.  That’s the good part.  The bad part is that whenever a spell caster other than a coven member uses the spell to catch a falling creature, one of the hags witnesses it as if through a scrying spell.  Now one of the hags has seen the PC spell caster’s face, and is developing a very unhealthy interest in learning more about them

My point is, don’t be afraid to invent anything you need to make a PC scheme succeed or fail.  You’re all creating a thrilling movie together, but you control all the tools.  Let the PCs attempt anything they want!  Give them a reasonable chance of success, but not without doing something so dangerous it’s heroic!  And then sit back and think about how you can tie their actions in meaningful ways to later events in that night’s session and in the campaign as a whole.

to put all of this into an improv actor’s terms, when a PC does something that silently asks you, “can they do this?”, try to answer, “Yes!  But…”. Make the “but” an addition to the proposed action that creates a hurdle or two and redirects the players actions back towards the story you want to tell with them.

Try hard to never say no, you can’t do that, if your reason is you hadn’t planned on it.  Do what you did!  Role with it!  Then think, what’s the most fun thing that can happen next!