That’s a great way to get started! Offering free proofreading for authors helps you build both experience and confidence. You might also want to practice with sample texts or style guides to refine your eye for detail. A helpful resource is Reedsy’s guide on proofreading basics: https://blog.reedsy.com/proofreading/
With a 3.0 GPA, UofT grad school might be a stretch but not impossible if you have strong references or research. If you’re not into other Canadian schools, focusing on getting a good job first makes sense—you can always revisit grad school later with more experience. US/Europe could be options too if you’re open to studying abroad.