Hi Katie_h17, I didn't major in SLP and still got into a grad school. There are a lot of programs that offer prereqs for those entering the grad program without an undergrad major in SLP. For my program, I had to take a few prereqs before officially being enrolled. Thankfully, I was able to get a deferral for something else and used the remainder of the time to finish up the prereqs. As for changing majors, I don't know if that is really necessary, because many of the required classes for education majors also apply to SLP prereqs. I took education psychology, language development, and statistics in undergrad--and my friends in the education program were also required to take these courses for their major. These three courses are definite prereqs for any SLP grad program. The more specific courses, such as: intro to audiology, anatomy and physiology of speech and hearing, speech and hearing sciences will have to be taken on your spare time. And they are quite easily accessible through online programs. I am currently enrolled and finishing up on three of these online courses. It was really easy to get into and started right away.
And with these prereqs already finished, I only have to be in grad school for two years like everyone else who was an SLP undergrad major. Personally, I would take some summers during undergrad or even taken less units in school to enroll in online or community college courses that are more specific to SLP. This way, you are able to shave off anywhere from a quarter to two years of school on top of a two year grad program.
Not only will you be able to save time by taking SLP courses during undergrad, you can also be a more favorable applicant to the grad schools you'll be applying to. They'll see you already took the initiative to plan everything out and did not make a last minute decision to become an SLP.
Hope this helped a bit! Wish you all the best!