Bayer is just the brand hunny. They make aspirin, but if you read the ingredients there probably isn't aspirin in the alka seltzer. I think it will be fine if L&D said to take it.... I couldn't if I wanted to though, makes me wanna puke just thinking about it!
My doc said no alka-seltzer :/
I take a tums knock off brand with calcium in it from the dollar store. The added calcium is actually good for you. Im sure just taking one wont do any harm but I would buy something else if you arent sure. And if youre worried call l&d back to be safe.
I'm not sure of the risk or anything, but it might be a good idea to call labor and delivery again and just tell them what happened. I'm sure they will tell you if it is okay or if they want you to come in. Good luck.