A bad essay grade has me drained.

I'm in my third year of college and have never gotten below a 75 or a C on an essay. However, my most recent essay got me a score of 65. I asked my teacher what the issue was and most of her notes were that I had incomplete sentences and strayed too much from the overall topic of my essay. I am asking for some advice on how to combat that. I know that I am not an awful writer by any means but I also know that improving constantly comes with the hobby. I am open to all advice, especially because I really want to become a better writer overall. Considering that is my degree and all lol. Thank you guys!