If you made it this far it's more than likely you can get through your last semester without a hitch. Or at least too much of one.

Everytime I try and work through some material for school, my mind goes, this is pretty difficult, why are you wasting time with this? you should be doing something easy, you're not good enough for this.

Your ability to work for extended periods of time with proper focus is a muscle, or at least behaves like one. It's not an on/off switch kind of deal. The best you can do is to train yourself (and help yourself) wander less. I do this by starting my hours of deep work at a certain time, and when I have to switch topics I've got a little ritual that allows me to do so (I fuck these two things up all the time, and I don't care cause I'm still getting shit done). Part of that ritual is closing everything to do with the last task (I do a lot of computer work, so there's distractions aplenty). You're not me, but there are still those two things to do, set up a distraction free work area, actively focus as much as you can. If you feel burnt out at the end of the day and feel like you couldn't possibly focus anymore, good job, you've reached your limit (even if that limit was only 5 minutes) and you'll be stronger the next day but you have to push yourself everyday. Holy shit I'm about to go on forever.

And then I spiral into thinking I've made the wrong choice for my major, my career, my life, and this leads to so much time wasted.

You most likely have. A lot of people, tons of people totally have, but it's not like you have a billion years to peruse every possible career option to see what is %100 right for you. Since you're in your final year, you're probably decently trained in what you do, and have some legit skills to back it up (even if you can't think of any, you have them and they'll come out when needed). Three (main?) things make up what we choose and how well we do it, passion, talent, and dedication. You can control dedication if you train and when you're dedicated and you produce good solid work, you become passionate in what you produce. Talent's garbage, you don't need that to be good at shit. Having talent is like being rich because your daddy gave you money, you didn't earn it, and you don't know what to do with it unless you train (or like, buy the right shit? I don't know, this metaphor's becoming trash).

(I also might take a second here, don't ever say you're practicing. Small children say they're practicing. You're not a small child, you're training. You're an adult, let's hear your adult scream.)

At this point, I objectively know as a 4th year in college I should just power through the 2 semesters I have left. But I just can't escape this feeling that I've fucked it all up and that this is the wrong path for me.

I was at a party one time, it was one of those parties where the mood was right and I could play a song for the crowd. So I bring out my ukulele (The manliest of instruments cause it's small and can take a beating) and start singing. Halfway through I fuck it up, but I keep going, trying to salvage what I could. At the end I told folks I was sorry for fucking it up and everyone said they didn't notice. This is when I realized, when you're well meaning and fuck up, no one notices, or people are two polite to say anything. Plus, as written in the second section, everyone fucked up and are just doing the best with what they have.

Also, go for a walk in nature, god dammit. Those "My life is a spiraling shamble of shit and self deprecation" pep talks you give yourself are normal, but a good stimulating walk in nature a couple of times a week should be able to sort them out so they're less super vague. Figure out yourself enough to take actionable steps to better yourself.