I think you're probably typical of an Instagram user, in that you can easily feed inadequate and down, viewing all those perfect people, with perfect lives doing amazing things.
But it's their highlight reel you're watching - the PR'd version they want everyone to see, not their reality.
But you're one step ahead of most on Instagram, in that you know yourself well enough to realise how it's affecting you - and have the willpower to step away. This is a healthy position to be in, so I wouldn't get too down.
You are the sum of the people you surround yourself with - which counts online too. Just try to weed out the fakes and be mindful of taking everything you see with a pinch of salt and you'll do better than most :)