Expressions: Glad you like it. I guess

[Learning_English]

A: Would you like to have an apple?
B: Oh yes please! I love apples.

A: Well, there's a big one and a small one.
B: Oh, I will have the small one.

A: Are you sure you won't have the big one?
B: No, Thanks.

A: Glad you like it. I guess. I will have the big one for myself.

Here, I guess refer to which guess?

Also, is it `glad you like it' = I am glad that you like the small apple?

Please clarify my doubts.
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Please let me know if I have made any mistakes in any of my sentences.

[Pamela]

Hi Learning_english,

I guess=I suppose, I believe

[Yankee]