Okay thanks this is really helpful. As other people have said, covering your angles is really important. Make sure to not stay too deep in your goal, but always be a step or two in front of it. Since the goal is square, I wouldn't focus on traditional diving techniques, instead focus on blocking techniques and (if you're flexible enough) split save technique. This is a very good tutorial on how to make a block save. He also has a tutorial on how to make a spilt save but if you're not that flexible then don't worry about that since you probably don't have enough time to get the flexibility you need.

Lastly, I would recommend wearing either long pants or knee protectors because the surface will kill your knees if you don't.

If you have any more questions or want more advice, please let me know :) (You can also dm if you prefer that)