Guild Wars 2

I have received all of my in game bonuses, but do I still need to find my serial code and save it so I can play HoT on release? And if I have lost it does that mean I won’t be able to play the expansion? Thanks in advance!

If you upgraded and received the items for the the expansion plus the beta slot then you are indeed upgraded to HoT. There is nothing else you need to do and you will have access to the expansion when it is released. However, you may want to try to track down the serial code that should be in your email if you bought from the in game store or the web store. It is a valuable piece of information to have should you need to contact customer support and they ask for it.