Is there any way to know we are not at the center of the universe for sure?
Maybe, it depends on whether you want to know if it is possible to do at all, or if you want some easy demonstration which could be used in a discussion.
I don't know any convenient method of checking which could be done at home but it should be theoretically possible to do, although it might require more advanced technology than we possess today.
The common theory which says that the universe lacks a center says that it is shaped like a four-dimensional sphere (or torus, or saddle) upon whose surface all matter and energy is stuck. The curvature of the sphere (or torus, etc) then means that two really long parallell lines will meet, eventually.
Their theory says that they will not meet.
Then it should be possible to test this using two, very finely aimed, parallell laser-beams. If they meet (or possibly diverge, the torus might have that effect) then that should prove which theory is wrong.
The only problem is that the beams may have to be several light-years long.
BTW, their argument about how the universe must be geocentric (or almost so) because we can see uniform amounts of galaxies in every direction is bogus. They are uniformly distributed around us because they are uniformly distributed all over the universe.
The argument about how all galaxies appear to be ordered in concentric spheres of different redshiftedness around us (and that they therefore are all moving away from us, as though we were the center) is bogus as well. The universe seems to be receeding from any given point in space, just as all dots are receeding from any given point on the surface of a dotted, inflating balloon.
I didn't know if you knew this, sorry if you already did.