The mouse sensitivity is just one small thing. Your mouse might actually be bad, your keyboard might be bad. Your aim is certainly bad and your game sense for sure. What you can do is go to r/mousereview and ask for help in order to choose, a proper gaming mouse for fps.Yes not all gaming mice are the same and not all gaming mice are good for all genres of gaming.
They will ask you a bunch of questions (grip style, hand size etc.) and they will recommend to you a great fps mouse that you need to buy once and you will probably have for many many years. As for keyboard i would suggest you pick up a mechanical one over a standard mebrane one to elliminate input lag and also have something with n-key roll over (registers every key pressed as opposed to 3-4 max keys of standard membrane keyboards).
Now in order to improve aim you just have to go to practice range and practice. Warm up before you jump into the game. Try to get headshots while moving, crouching etc.
Finally for game sense you can watch a few streamers play the game on twitch. I suggest medium known streamers over big ones as big ones always play in premade teams (with friends) and are talking over discord very little since they have been playing fps together for years and do not need a lot of communication to achieve their goals.
In time you will get better. Also keep in mind that when you do not know what you are doing (in an BR) it is better to avoid hot-dropping (dropping in areas with lots of opponents). Take your time, loot (don't stay in one area looting for too long 1-2 minutes is usually enough) and keep moving from cover to cover with your squad. Remember communication is key. Do not assume that they saw the enemy you saw, do not assume they do not want that weapon that you just found, do not assume they got your back or that they pay attention to the surroundings. You got to do all those things and communicate them to them. Mark the enemies, highlight the weapons, ammo and attachments that you come across and you will do just fine.