Live and learn. And start over. With better quality materials than junk from floor and decor. All of those bargain wood tops are terrible quality more glue than wood.

A sprinkle isn't enough to cause severe warpage. Place a straightedge on them and measure please. Clean the adhesive off the surfaces to be joined and reglue it. Titebond 2 would be fine. Maybe rent some bar clamps?

I agree with Joe, a sprinkle didn't cause the problem.

Joining large panels can be challenging. The two edges to be joined need to be square and clamping needs to be done in a way that keeps the panel flat while the glue is curing. You'll need to start by cutting the panels at the joint and starting over.

Pictures would really help advise you as it is difficult to give advice without actually seeing the severity of the problem. You can probably clean up the problem.

First, dowels, biscuits, dominos, etc. help with alignment and add strength when you are doing endgrain glue ups. It is doubtful they are the cause of the problem and doubtful they would have corrected it. Glue alone is plenty strong enough for gluing two panels together.

Next, your counters are going to get wet, in fact sealing them is largely just wetting them, and they aren't going to warp. It is doubtful the warp was caused by the sprinkle.

Pipe clamps are fairly cheap and worth investing in for a big glue up, but ratchet straps should work for gluing two panels together. However, you have to use clamping calls when gluing panels or they will lift. For gluing two pre-glued panels together the calls would be incredibly easy to do, just a few boards at the glue line with longer boards clamped for pressure.

If the problem is the single glue joint, the easiest thing to do is rip them apart and reglue them. A thin kerf saw blade is 3/32" thick and an ultra thin kerf or micro kerf saw blade is 1/16" thick. You can rip them apart, square up the edges and reglue them with proper clamping calls and only lose about 1/8" (1/4" sacrificed would make it easier).

If you can't afford to lose 1/8" they can probably still be flattened with a router box flattener or a hand plane.

Again, pictures would help advise you.

Cauls.

Autocorrect...

How thick is the BB & did it have any finish on it before the 2 sections were glued together? Did the friend rip the edges to be glued to get to fresh clean wood before glue-up?

Pictures?

Odds are that the warping was caused by the glue-up and not a bit of rain. Need to use parallel clamps or cauls if using bar clamps. And clap from both top & bottom.

Like they^^ said, the top can be salvaged by ripping at the glue-up line and re-gluing and proper clamping procedure. I agree that dowels, biscuits, floating tenons are not needed.

What biscuits, floating tenons, etc. do is help keep the top surface of the two panels aligned at the joint. That minimizes the need for anything other than a light sanding after glue up. That, in turn, helps to minimize the foul language in the shop which might otherwise accompany removal of the clamps. I alternate clamps top and bottom and use a straight edge to check for any cupping, twisting, etc. before the glue sets.