How do I correct a public yes to a proposal when I wanted more time?

My partner proposed at a dinner with our friends. People clapped before I'd answered. I said yes, hugged him and spent the next hour smiling for photos.

We have talked about marrying someday. We haven't talked through what that would mean for us now. When he asked, I was happy that he wanted me and overwhelmed by the room at the same time. A day later, I told him I wasn't ready to call us engaged. He said he'd understood our earlier conversations as agreement that we were ready.

I don't want to end the relationship. I want to return to the conversation we hadn't finished. He says he can wait, but is embarrassed about telling everyone the announcement was premature. I feel awful about that, especially because I did say yes.

How do I take responsibility for the answer I gave without treating it as a decision I must now keep? We need to tell our friends something, and I don't want them to become judges of who misunderstood whom.