I just unlocked subclassing for the first time and I’m very confused..

So it says upon reaching skill rank 50, a skill line is considered mastered and no longer counts towards my subclass limit. I am a magplar. I want to have Puncturing Sweeps, Radiant Glory, and Channeled Focus which is a skill from each class ability. I do not have any rank 50, but if I get them to rank 50, can I still keep my 3 skills from each class and use a subclass?