Ok, then I guess I can recommend Introduction to Quantum Mechanics, by David J. Griffiths. Itās not a complete book (as youād expect an introduction book to be) and Iāve met many people that shy away from it because of that, but I believe itās the most instructive book out of the undergraduate quantum mechanics books. I remember the first time I came across sums of angular momentum and only being able to understand it through Griffiths. While youāre at it, you might want to try Introduction to Electrodynamics, also by Griffiths, as that one is pretty much agreed to be the undergraduate electrodynamics book, at least from where Iām from. Just a warning, this one is more math-heavy. That same guy also has a book on particle physics called Introduction to Elementary Particles, but this one I have never read, so I canāt vouch for it. I heard itās pretty good, though.
About āspacetimeā, I believe what you want to know more about is special relativity, since general relativity is quite advanced even for an undergraduate student. Iām not the best person to recommend special relativity books as I myself havenāt found one that I adore (and I consider myself much more well versed on quantum mechanics than on relativity), other than the last chapter of the electrodynamics book by Griffiths I just mentioned (you can tell I really like this Griffiths guy), as, believe it or not, special relativity was inspired by electrodynamics. Some people have recommended me Introduction to Special Relativity, by Robert Resnick, but I canāt recommed it since Iāve never read it (someday, maybe), so take it as you want.
I know realized I only mentioned books with āintroductionā on the title. I guess thatās a good thing. Also, I wouldnāt recommend you to buy those books, as from experience I can tell they can be quite expensive. Try to borrow them from a library or something. Happy learning to ya. :D``