Do what you love. You are only going to be in high school for a short amount of time and if you truly enjoy playing softball, stick with it. Does your school offer nursing courses? You can most definitely take those types of courses and play softball at the same time if it allows. I regret quitting baseball in high school to concentrate on something else and for that reason, I fully recommend that if you love playing softball, you should stick with it and play throughout high school. You will not question yourself later in life if you do this.
The good/great news is that you can always focus on multiple things if you put the hard work in. I myself played only baseball in high school and ended up playing a year of basketball in college as a walk-on. Also, I focused on Psychology/Cognitive Science during my undergrad and then got my Master's in Sport Management. You can use high school to start gauging your interests and path, but there's always room to pivot or have multiple interests. What is also important is understanding how far to push yourself and how you work/learn. This is the secret life lesson to college: figuring out how you as a person work and how you learn.
Be open to all possibilities and work hard!