The Soviet Union never abandoned its long range goal of world domination, the only question was a tactical one of how to achieve this.
Why did he invade Finland? Was this all part of "socialism in one country?" ===
WHY? It was preparation of world war. He wanted to move border somewhat farther of Peterburg. He decided to do this on account of Finns. Since those Finns was one of few nations collaborated with commies before.
It was done as everything done by Stalin the dictator. It was unjust.
But in frames of discussion of Did he want or not to export socialism I rather say he didn't since his enemy Trotskii who was ideological exporter.