I love McCree, he's my most played hero and he can be a lot of fun. (PS4 player here).

McCree's problems are that he's very team reliant because of his limited mobility, relatively large hitbox, and limited range when compared to other hitscan heroes (Ashe, Widowmaker).

That being said, you can also be effective with him provided that your team backs you up and you use good positioning as often as possible (finding natural cover in the map, maybe even peeking corners, staying close to your supports).

It could also help you to learn various other heroes to find out how to beat them. For example, Genji can deflect McCree's ult and D.Va can block it. However, Deadeye can also generate enough damage to instakill, making Zenyatta's ultimate pointless or even causing a shield to instantly shatter. The more you play, the more you'll learn. Keep at it!