you need to anticipate enemy's movement and stay alive. CS are team-based game .
1. cut off unnecessary voice communication.
2. be unpredictable. make sure to use sound as your partner and your weapon. when you're one on one situation you predict the enemy's movement. you can even fake that you are rushing from the vent on dust2 B site by making a fake jumping sound and quietly walk through the door.
you can even do simple mental trick like when you peek on catwalk and the enemy is on the green box near the dark-side T-spawn on dust2, you can predict his habits by counting how much bullet-tap shots hes doing before you peek. for example you make a fast peek and one bullet shot to warn him purposely and he'll start shoot tap at you. if he's doing triple shot, count to three shot and do a short peek shot AND slightly place your crosshair to where you think he's going to strafe.
make sure you're not strafing to far from your hiding spot in case if he's anticipating your movement.
3. stop rushing and being aggressive unless you have a good position(upper indoor stair on inferno against T-side on lower part of the stair) or crazy aim. remember 5 vs 5 is easier than 4 vs 5. simple math.
4. do mind trick, place yourself in steady places and even unpredictable one such as holding dust2 B site as CT. You sit on the box peeking between the door facing straight to the brown "X" box in the middle of the site. no one will be expecting you to be there.
5. train your movement. I know it's silly but bunny hopping, ladder climbing and moving in the heat of hold rush from T-side are critical..
I guess there's many thing I'd like to talk about but it's 12:24 AM. night bro. goodluck
Edit: remember it's not that your aim suck on scrim. You just feel the pressure being in competitive mode . It's normal, we all have that.
Learn how to use flashbangs. Seriously. Especially as a ct. Most pub dm stars don't buy them or die before they do. If you see a 5 man rush coming b don't run like an idiot. Run, but chuck flashes. Seriously just throw 2 right in the middle of the site, on the ground is fine they will be like watafak. This allows your teammate to rotate faster and usually slows bomb planting by at least 5-10 seconds.