Step two: figure out why your performance didn't meet your expectations.
Bismarck's advice was all spot on with what I'd suggest. I'd add that you need to be willing to be brutally honest with yourself. And if you can't be honest with yourself, don't expect anything to change.
I've seen one person after another go on and on about how the teacher set them up to fail, or their job set them up to fail, or etc etc - excuse after excuse. When I'd probe into how they studied, it would turn out they just plain weren't doing the work. They weren't showing up to class prepared, or they weren't taking good notes, or they were focused only on finding the 'answer' to homework instead of deeply understanding the problem (I have in mind a particular physics study partner for that one; she'd do great on the homework because she'd find the right 'formulas', but she didn't have a cognitive understanding of the problem or solution so when she'd get to the test and encounter a slightly different question she was hopelessly lost.).
If you are really, honestly putting in enough quality study time, you should not struggle to maintain better than a 3.2 in undergrad in my opinion. There are exceptions (learning disabilities, life events, schools that are trying to flatten the grade distribution, etc), but in my experience 9 times out of 10 when someone doesn't perform as well as they want, it boils down to not putting in enough effort.
In your specific case, I wonder if you can work two jobs, volunteer, take two science classes plus calculus, and still find sufficient time to study for those classes. That may be biting off a bit more than most people could chew.
Find out what resources your school has to help you improve. Taking advantage of them now when your GPA is easily salvageable would be a lot wiser than waiting until your junior year.
Last, though obviously you want a higher GPA to get into vet school, a 2.9 isn't, you know, akin to failing or anything, and people get into vet school with 2.9 here 'n there. You didn't flat-out fail out of school (like, ahem, some of us have). So don't be too hard on yourself. Look at it as an opportunity to make some changes to meet your goals, and congratulate yourself on still being in the game after your first post-high school semester.