Did you put the thermal pads on the underside of the backplate? I would have to test mine as I usually don't fiddle around touching the card when gaming, but I would imagine, and especially if you are touching near where any of the power delivery is situated and has thermal pads, that there would be a lot of heat transfer to the plate.
The other thing to note is that touching the plate which is made out of metal has a much higher rate of thermal conductivity. This means that heat will both transfer to and from the plate at a high rate compared to something less thermally conductive such as wood or plastic/rubber. When you touch a piece of metal that is, say, 50c vs touching a different material the metal will feel warmer. What this means is that the plate can inadvertently feel a lot hotter than it is simply because more heat is able to transfer to your hand not because it's actually 'hotter' (although thermal capacity is a thing, so technically it could have more energy but be the same or lower temperature... I digress).
Ultimately I would say that if you can touch it and hold your hand there for a good little while you are OK. If you really feel the need some software (maybe EVGA depending on your card) can have additional thermal sensors to help you figure out why your temperatures are the way they are. An IR camera would be the best tool to use to determine the temperature, or even a laser thermometer or thermocouple but those can vary in accuracy. The 2080 Ti can be an incredibly power hungry card especially if you have modded the power limit, if you just keep pumping juice into it it can pull 450-500+ watts which means the heat has to go somewhere, and if it's not being dissipated by the block, then the backplate being warm is a good start in all honesty, as having it be cool to the touch would suggest no thermal transfer which means your components are either idling or cooking.
TL;DR: Warm plate = components are being cooled = happy