Flexibility,stretching questions..please help :)?

So i do taekwondo and i need to be flexible. Im pretty flexible myself but i still need to be more flexible. Im learning how to do splits now. Few days ago i went all the way down. My mussels were really sore the day after. They were sore for about 4-5 days. Now when they're ok i cant do the splits all the way down even though i do a really good warm up and trying to stretch but i can't reach. Did i tore a mussel or what? And i would like some tips/videos with a few techniques thanks :)