Yes, don't make gaps in the rail joints when using rail clamps. If your track is not secured to a ridged base, then it will move on it's own.
The Pennsylvania railroad had it's design engineers calculate the possible expansion problems with welded rail, back in the 1960s. The conclusion was that instead of the rails buckling, as some thought they would, the entire assembly would move sideways on curves. This action would take up any expansion issues on tangent track.