Thoughts on getting engaged/been proposed to?

I wanted to ask a question over people's potential thoughts when they got proposed to like what was your reaction/feelings when it happened?

Reason I ask is I wanted some advice or just other personal experiences that people have had.

Before we start its a bit of a read ᕙ(⇀‸↼‶)ᕗ I've put a summary at the bottom.

Now I'm the kind of person that just goes with the flow, I always have, if I really don't agree I do state my opinions but for the most part I try to make sure everyone is happy. So... My partner of 3 years proposed to me whilst we were on holiday abroad which I know must have taken a lot of guts for him to do it (he's quite a nervous guy). My issue is my reaction to it all, my first thought was "what?!" Like I'm assuming most people it comes as a surprise but it wasn't a positive what, I don't fully know what I was thinking in those few seconds but he just stared at me and was like "so?" With a nervous expectant face. I said "yes" Now like my partner I'm also steeped in anxiety and that whole shabang and I'm my head for the rest of the trip I'm just thinking "holy crap, what do I do" ive never been great at trusting relationships (because of past experiences) and I put my feelings down to that thinking that I could push past it and get on with this new part in my life.

A year and a half later we are planning the wedding I've booked a venue got a dress etc and I'm panicking. I'm incredibly worried that I'm being silly and jumping into something I'm not ready for. The whole process of organising the wedding I'm not looking forward to any of it, even the dress shopping I just couldn't get into. I kinda feel like I know the answer in my heart but I'm scared that I'm being stupid, scared that I'm going to get rid of a relationship that I've been in for years now just for some doubts. He's such a nice guy as well, we have small fights like everyone but never anything serious, there's genuinely nothing wrong, I'm just worried that he loves me and I'm not sure of my feelings back.

Long story short...

I got proposed to panicked waited (way to long) thought I'd be fine and sort my self out. But still panicking... Help... ( ･﹏･)