This is my first baby and we found out the sex at our 20 week scan, and I'm so thankful we did! It was a decision we literally made there and then, in the room!
This is going to sound awful - but leading up to that point I really struggled with my emotions and had some really low thoughts, to the point where I scared myself on a few occasions tbh. I began to freak out majorly about becoming a Mum and not being ready, and mourning my child-free life. Stupid and selfish I know
For various reasons it's been a tough start to 2019 too, which didn't help with how I was feeling.
By the time the 20 week scan arrived I was an emotional wreck and consumed with anxiety to know that baby was healthy, etc.
I don't know why, as we had always said we thought we wanted a surprise, but in the moment we just looked at each other and knew that it felt right to find out the sex, so we asked 
I literally felt the weight lift from me in that moment, along with all of that anxiety and those worries.
Since knowing about baby girl I've felt completely different, (it isn't because she's a girl at all, I soooooo just want a happy and healthy baby, regardless of the sex!), but it's allowed me to bond with my bump more. I feel so protective over her, I just love chatting away to my belly!
We are moving house in a few weeks, the new place needs alot of work, so it's also nice to know so we can sort her room and stuff 
I've experienced alot of judgement from people about the fact that we've found out though, which I wasn't expecting. It's our baby and our choice as far as we are concerned!
The thing that gets me is when a stranger in a shop says, "ohh do you know what you're having!?" so you tell them, and then they go.. "ohh gosh so you found out then? Hmphh well I wouldn't have done!" and practically tsk at you!
I swear they only ask what you're having so they can catch you out and sieze the opportunity to pass judgement, it drives me mad!
Anyway, longest post ever, sorry! Good luck OP for your scan and whatever you decide
xxx