The Pre-Engagement Ring Finger

I just got a pre-engagement ring from my boyfriend of 5 months. He`s 21 and I`m 17, we talk about marriage and moving in together this September. I had a lot of stress figuring out which finger to wear this ring on...so many different aspects to think about. For example, if I size it to my left ring finger...I wont be able to wear it with my engagement ring...so I talked to a lot of people who gave there opinion and the jewelery store...it`s wherever you feel comfortable. Now a days...there really isn`t a set finger for anything like that.