Alliekit, I'm so sorry to hear how sad you're feeling. While it's great that you're engaged and that's the main thing, I totally, totally understand you and get where you're coming from regarding your feelings about how it came about. There is nothing wrong with experiencing feelings of let-down that something didn't go the way you had hoped it would or even knew it was planned to go.
As described up-thread, my own proposal was the same, just "talking about it" and "might as well" stuff. Even though it shouldn't really matter, it's not exactly the stuff of dreams, lol. "Might as well" never feels that great.
I get the feeling you probably already know that it's fabulous that you're engaged and that's something to be happy about -- I don't think you need that information, lol. But I do think it's legitimate to feel sad that things weren't how you or even your boyfriend originally planned. Don't feel bad about feeling let down by the method. You already know that in the big picture it doesn't matter. But it's not shallow to wish it had been more memorable, especially since you know there was already a plan for that. It's not shallow, it's just human, and as humans we all mostly have mundane lives and there's nothing wrong in hoping that some moments, just some moments, might be a bit less mundane just for fun and memories. That's not shallow, just wishes for a few stand-out moments, and we all need those.
I hope you feel better. Perhaps --- and you needn't do this if you think it will hurt anything -- but perhaps you could take your fiance to a place you both love and which means something special to both of you. Secretly (or not secretly) bring some champagne-type drinks or a nice picnic, and then say to him that since you guys didn't get to have a special setting for the big question, lets do it over now just for fun. You could be playful and slip the ring into his jacket pocket while he's unaware, and say hmm, is there something in your jacket I might have mislaid? Get him to ask you all over again in the special spot, making it playful and light and sort of "go on, ask me again, but all special this time!" It might be fun even though you might both feel silly. Then you'll have that story to tell "Well it all went wrong in Venice but then I made him take us out to this lovely beach we like in Cornwall, and I egged him on to do it proper-like'"!