My DD had a GA at almost four months old, and then another one five weeks later. It totally freaked me out. The night before, I was an absolute mess. But she was fine and we had a wonderful surgeon and anethesist who helped keep me calm (they came out straight away to tell me what when on and that she was okay). She had an MRI one week after the initial surgery - they didn't give her a GA, just a mild sedative. She had to drink it, and then it made her doze off. They put earmu*** on her and took her in. She slept right through and was awake again about 20 minutes afterwards. She was a little groggy for the day. The worst bit was waiting. I didn't go with her into the MRI so I was just pacing the room until she came back. Good luck, and I hope all is okay

ETA - Wanted to add that the MRI in our case was quite quick. She was gone for about 20 minutes.