My (31F) boyfriend (30M) wants my engagement ring to be a surprise

Me (31F) and my boyfriend (30M) have been dating for 3 years and we are ready to get engaged. I asked him if he wants to go ring shopping together and he said no because he wants to pick the ring himself. His reasoning is that it’s supposed to be a gift from him to me and he wants the ring/ engagement to be a surprise.

This makes me a bit nervous because this ring is something I intend to wear pretty much every day for the rest of my life. I poked and prodded a little for details to see if he was on the right track. He described what he thinks I would want in a ring and I have to say, he DID pretty much hit the nail on the head with his description. (Keep in mind, I didn’t know much about engagement rings and hadn’t done any research at the time of this conversation. So his description was a general idea and not specific dimensions, cuts, carat, etc.)

A few weeks later, he decided to show me a picture of a ring on a website. It was very pretty but the cut is not a cut I have ever pictured myself wearing. It was a princess cut. I always pictured myself with a round cut. It WAS a really pretty ring though and if he proposed with it, I think I could potentially fall in love with it.

Fast forward another week, he said he needed to know my band size and how many carats I wanted. I had no idea so I told him I would go to a jewelry shop to get a band size and try on some different carat sizes to see what I like the most.

While I was there, I tried the princess cut but it just didn’t feel right. I tried round and cushion cut and those felt most like me.

After visiting the jewelry store, I had a much better idea of what I wanted than when we had the initial conversation. I tell him about my experience at the jewelry store and he was really receptive. Later that night I was scrolling some rings online and decided to show him some examples of some rings I found pretty and some features of other rings I didn’t like. At this point he started to get a little annoyed and went back to saying he wants to pick it and to just trust him.

Is it selfish or shallow for me to care this much about what my engagement ring looks like?

TL;DR:
My bf wants to surprise me with an engagement ring and insists on picking it himself. I went from “I trust you!” to “Wait… maybe not a princess cut?” after trying rings on and realizing what I actually like. When I showed him examples, he got annoyed and said to just trust him. Am I being too shallow for caring this much about the appearance of the ring?