How do I apologize and show more appreciation towards my boyfriend?

Today after school, my boyfriend asked me to accompany him to the mall because there was something that he needed to do.
I agreed and once we got there we entered a jewelry store, there he told me to look at jewelry and tell him what I liked most. I asked him why, then he tells me that maybe he’s thinking of what to give me for my birthday (which isn’t until May).

I told him that I didn’t want anything expensive but he insisted so I just went with it and chose a pair of earrings. Then and there he picked them and paid for them… I was a bit shocked, but otherwise I was very thankful and grateful that he would want to spend that much money on me (to me the gift was very expensive). I told him that I was thankful and since we were in public I rarely display my affection by kissing especially. Though he asked for a kiss and I gave him one, afterwards he tells me that I’m not very appreciative (mind you, this is the second time that something like this happens and the word, “appreciate” is said) so I got a bit hurt by that.

When we got home I tried talking to him but he seemed very frustrated and so I just kept quiet instead of quarrelling about it. Now I’m thinking of ways that I can apologize for the way that I acted earlier. Can someone please help?