When you shoot a gun, it gets hot. It's simple physics. The cold bore zero will differ form the point of impact when the bore heats up. How much it varies is different with different guns. The lighter the barrel, the quicker it heats up, but also the quicker it cools down.
As for floating the barrel, that helps with barrel harmonics, and deflection of the barrel when using a sling or bipod. It really doesn't help with heating of the barrel.
How much are your groups opening up? In inches or centimeters.
Your rifle will have 3 basic points of impact. One when shooting from a clean cold bore. One when shooting from a cold bore, and one while shooting after the barrel is warmed up.
Keep a log book, and figure out what the difference in POI is on these. Then when figuring out your group, either let the gun cool completely, or dump your cold bore shot into the berm or similar, and then shoot for groups.
Also have patience and don't overheat your rifle. Shooting for accuracy requires patience.