I'm also a very passive player, but when I play PUGs i just force myself to be aggressive. I don't have much confidence either, but just fake it until you make it, because it works.
The only thing you should be learning from the pros at your elo range are different nade lineups and solo plays. Maybe a nice self pop flash that you can use a couple of times a game or some cool unknown one way smokes.
I started overestimating my opponents (after watching pro players' games) which is why I never made any solo plays or took any risks.
4v4 on inferno and you're playing on B as CT.
You and your teammate are playing site, but you don't hear anything in banana (no flashes, nothing). With my old passive and non confident mindset I wouldn't try to peek banana, because after watching many pro games I'm expecting someone to be holding for my push/peek.
But trust me, a lot of the times no one will be holding banana. Instead they will be top mid and second mid baiting each other waiting for someone to go first. And just like that you can get 1 or 2 kills by flanking them from banana.
Sure, sometimes there will be someone holding for your push, but that is a risk you have to take. If you're afraid to dry-peek, you can ask your teammate to flash for you, which will increase the chances of you winning the duel in banana if there's someone there.
Now obviously there is a time and a place to make these plays. If you're up 5v4 or 5v3 one could argue that you shouldn't make that kind of play because you might just give them a free kill and thus a way back into the round.
But if it's a 3v3 or 4v4 you could do it,because they can't hold every single angle/position with just 3 or 4 players so you might be able to catch a nice timing and make a round winning play.