Hello! I am a platinum support main - I would be happy to give you some advice. I'll try to cover concrete things with specific goals, rather than 'ward more' .. ect ect.
1.) Any champion can take you to gold in my opinion. Over 90% of the cast can take you to platinum. I am a believer in playing a single champion very well. Keep going with Cass, and get your build down. Your thoughts should always be on the game, not on what your building.
2.) After checking your profile, the single biggest thing you can do to raise through the ranks is to die less. I know that seems basic, but I notice that on many of your games, you die over 8+ times. I want you to start focusing on dying 5 times or less on each game. This will teach you to be a SAFER player, and that is a critical skill to rise through the ranks.
3.) If you have advantage in lane, and have killed your opponent once or twice, do not be afraid to roam. Cass can pull of some terrifying initiates with her ultimate - a trip or two bottom post level 6 can be huge. Especially if your BOT lane is struggling.
4.) Always be looking at what champions are buying, and how many deaths/kills they have. Always have a rough idea of how powerful a player is. If top is getting fed, you should know about it immediately. If someone is fed - stay away from them and only fight them as a group.
5.) I feel like you are doing this already, but make sure your focusing on your own play, rather than if you win or lose. Did you play the match well? what could you have done better that game? Do not look at if you won or lost. The best of the best lose about 40% of their games, so don't think that a loss means your a bad player.
Hope it helps - goodluck out there!