When I bought my keikogi I felt exactly the same! New keikogis are always too big and unconfortable, but believe me, with the training and washing it will get smalled and it will adapt to your body
I know it's hard to believe, I didn't believe it either, I wanted to buy a smaller number, but now I'm glad I didn't! And you are 14, you're still growing so it's ok if it's a little big for you.
Before you know, you'll want to wear your keikogi all the day hehe