15 Y/o Male with some questions

I haven't been in a choir class since 6th grade and I auditioned for an advanced musical theater class (basically the alternates for core) as a tenor and my instructor said that my voice is still developing. I can manage pretty high notes but now they moved me in bass and I struggle in class because I can't hear the basses (I have to match my singing with them since I'm fairly new). I'd like to go back to singing tenor. Is it possible? If so, should I work on improving the range of my chest voice? All the other tenors in my class can reach a good range using chest voice and I had to use my head voice. Also, how do you practice the transition between chest voice and head voice? I can sing low to a bit of a high chest voice then when I transition to head voice it's too high. I can't seem to hit the notes in between.