I used bitcoin wallet generator (app on phone) to make a public and private key

I used bitcoin wallet generator (app on phone) to make a public and private key. I didn't store, I just wrote it down. I have never used it and I am only person who has ever seen it. Could I now but some cryptocurrency on coinbase and store in on that private key? Basically it's a paper wallet, I think? New to all this and want to be sure this is safe?