iPad Air vs. Macbook Air for university?

Sorry for the huge chunk of writing! TL;DR: I bought an iPad and don't know if I should return it and get a Macbook Air. More details about my whole situation and dilemma can be found below.

I bought an iPad Air recently and went through a lot of hassle because of it (long story...) but I finally resolved everything on January 2nd and was very satisfied with it. A few days ago the new semester in my university began and here is my current dilemma: I have a computer science class this semester in which everyone uses laptops. I have been writing on paper the past few days and although it's not the end of the world, it would be much more convenient for me to have a laptop to bring with me to school since the compsci prof loads up files from the course website and writes on them, which is also what everyone else does in class along with him (except for the 10% without a laptop). Having a laptop with them allows the students to do what the prof is doing right there and run the files to test if they're being done right. I asked the prof yesterday he recommends bringing a laptop to class and he said that I don't have to, and that the final will be on paper anyway so it's not bad to get used to it. But he also mentioned that near the middle of the course he will be "flying through code" so it will probably get a little bit confusing for me, but he added that I can always look to the person beside me since almost everyone has a laptop. A problem I've found is when he copy-pastes something and adds it in between something we've written previously, which is obviously impossible on paper and thus kind of irritating, and since the course will get increasingly difficult, it will get increasingly difficult to keep up on paper. That being said, I am writing this on my current laptop which is WAY too heavy to bring to school (I brought it once and had terrible back pains) which is the reason I bought the iPad because it is so portable. However, now I am finding that the iPad Air is quite limited in the things it can do and am wondering if I should return it (I have until January 16th) and buy the Macbook Air, which would be approximately double the weight of the iPad Air and half the weight of my current laptop. Or if I buy a keyboard case for my iPad, which I was planning on doing, the weight difference will be even smaller between the iPad Air and the Macbook Air. If I buy a keyboard case I will be able to keep up, but I won't be able to save files from the web page and I won't be able to run files to test them, so at home I will have to transfer all my notes onto my computer anyway so I can try them out (but I could keep them on the iPad for studying purposes). The positives of the iPad are its portability, and in a sense its lack of possibilities because it keeps me on task and prevents me from procrastinating, which is ridiculously easy and therefore very tempting on a laptop. Thus, I get more done when my laptop is not turned on. The reason I bought my iPad was to have lecture PDFs on it, textbooks, watch videos on the bus, take notes in class (after purchasing a keyboard, that is), and watch lecture videos online; basically to help me study and stay focused, which is why I like it. Some reasons to get the Macbook air would be to replace my current laptop, and to have something that's portable yet still very useful and that I can write and keep most of my notes on. One bad part, however, is that I'm afraid it will be too easy for me to procrastinate and go on websites like Facbook during class and during time at home spent studying. I'm not sure if I want to major in computer science; it's either that or psychology, for which a laptop probably isn't necessary and an iPad with a keyboard can do, but I'm not sure which option will be more beneficial in the long run. The price difference between the iPad and Macbook is $426.71 and the Macbook Air would clearly be the better option if I had no laptop, but since I have one and its only problem is its weight, I'm having an extremely hard time deciding. There is no chance for me to bring my current laptop to school since I get terrible back pains having it in my backpack. Another option would be to get a cheap laptop for approximately $400 that I can bring with me to school and use exclusively for compsci, as well as psych since it would be easier to take notes with a keyboard for that class also, but then my iPad will lose half of its intended functionality. My question is, which of the two options would be better for me in the long run?