Considering the major switch

I am currently a freshman studyin mechanical engineering at a stem school. Due to complications with my summer courses and the compatiability with the school/finances, I am transferring to UCF in this upcoming fall 2018. I have been doing some soul searching after the second round of tests in my core classes and getting 60-70 at best (that consisted of weeks of studying but also I have test anxiety). My love for animals goes far beyond just wanting to help. When I was little I wanted to be a vet because I felt I had a bind with them (all other vet students must say the same) but ultumity i decided i may want to major in pre-vet because there was only so many volunteer hours i could put in at humance societies and so much money i could raise/donate to places who take care of all kinds of animals. Now that I have realized that engineering is difficult and my dad in fact is an engineer and told me it is apart of the struggle to understand the material. I just don’t knoe how michni truly care about any of it when it comes to post graduation. Where if I was a vet I could practically see myself enjoying at least half of the time I spend doing the job. I am trying to see how competitive the field is and how likely I would be able to get into a grad program. I have an army rotc scholarship but am currently thinking about not having it because I don’t knoe I ok can see myself in military anymore. I know there are fields for vets in it but I can’t come to a rational decision and need some insight. Help!