Don't worry about that. I think that if You don't speak a Slavic language they all sound pretty similar.

Until I hanged a bit with Spanish and Portuguese speakers (during my Erasmus stay in Stuttgart few years ago) and learned some basics of those languages I was conflating those two as well, despite they sound completely different (Portuguese sounds a bit like French mixed with Russian to me :P), but people conflate those two as their spelling and grammar is close. Now I get a bit irritated when I hear someone mixing Spanish with Portuguese, although it's common. Also a fun fact: Latino telenovelas are in Poland commonly referred to as "Brazilian", despite them being usually from Hispanic countries and just a few from Brazil.

I speak German a tiny bit, but I think I'd have problems distinguishing between i.e. Dutch and Schwyzertüütsch ;) ...or even some Nordic languages. Man, Schwyzertüütsch sounds really weird to me.