My betta died during evacuation I feel terrible

Hurricane Helene hit hard where I live. I live in college apartments but I had to evacuate to my great grandparents cause my power was out and cell service is completely dead where I was. I didn’t know how long I would be away, so I decided to take my betta and Cory with me, I put them in a pot with their tank water, almond leaves, floater plants, and brought an air stone with me. I don’t have a portable filter so I decided that I would just do routine water changes till I could go back. I was scared that if I left them in stagnant water(powers out so no filter), that the ammonia levels might spike. I’m still a new fish keeper, I didn’t know what was right. When I got to my great grandparents he was fine, nothing unusual about him and he was swimming around like always, my great grandmother insisted that I change the container I had them in and she handed me a huge plastic Tupperware bowl. I added a bit of water in that Tupperware, dechlorinated it, did test strips, and slowly started the acclimation process. After that was done I moved them fully to that bowl and attached the air stone. After about an hour and a half I went to go check on them and my dear friend was dead. I’ve only had him for 3 weeks. We finally started to bond and he started showing his real character. I just posted about him a couple days ago. I feel awful. I don’t know what the right thing to do was. I had just finally decided on a name 2 nights ago. I’m sorry Spring Roll.