How would you say "I changed my mind" in Japanese?

Question

I get the feeling this question might have a whole lot answers with no one, true correct one, but I've been really itching to figure out how exactly to express this in Japanese as there have been several times where I want to say it but I'm not sure how. I've been falling back to a really literal and simple of way saying it, which I don't even know if it's right but, as 「考えが変わった」which always feels horrible and weird to me whenever I say it, but I have to say something instead of just standing there like an idiot with my mouth wide open.

To provide some context, I was at 7-11 getting some oden, and I chose the smaller option trying to hold back on the amount of soup since I wasn't super hungry, but I noticed it didn't have enough room for everything I wanted. I first tried to think of how to say, "it doesn't look like it will fit so I'll take the large one instead," but I had no idea what "to fit" or anything similar was in Japanese, so I then tried to think of how to say "I changed my mind," but remembered I still have no idea how to say that, and fell back onto the above mentioned phrase.

As I said earlier, I have a feeling that how to express this in Japanese might heavily depend on the situation and might not have a set phrase like in English, but, for the situation I just described above, how would one express it then? If you could also tell me what "to fit" in this case is too, that would be lovely.

Answer 1

I think I understand your feeling, it sometimes happens that an expression that we are so used to using in English just doesn't exist in Japanese and it can be frustrating. 　

The closest you will get is probably 気が変わる. Which literally means I change my mind.

But in most cases, it's best to just explain the situation.
Using words such as やっぱり or 結局 can help you a lot.
You can often hear やっぱりやめた。(Giving up on what you were thinking of choosing)
You can also say things like 結局これにする (After all I think I will go with that one.)
There is also 考え直す which means you have reconsidered.

In your situation you could have explained and said something like:

結局入れすぎちゃったので、大きいサイズにしてもいいですか。

As for to fit, there are many ways to say it but I guess "合う" might be your best bet:

サイズが合わない