Theres a lot to unpack here.
First off, scripts do not work. Especially in defense style presentations like yours where you'll be questioned by an audience, a script locks you into thinking about your topic in one way. A master speaker can say the same thing 100 different ways.
For you to improve, you need to modify how you practice. Start small. Write down five key points you want to express in your presentation. Read them, then flip the paper over so you cant see them. Deliver into the mirror, trying to recall the five points as best you can while adding detail to each point as best you can. When you cant think of something, look at the paper for help, then return it back to hidden. When you say something you really like, make a note of it, then hide it. Repeat until you can repeatedly move through your main points with ease.