What is a day as a biomedical engineering like?

Depending on what specific job function it will vary but it is a lot of analysis using math, science, computer programming and potentially reading scientific journal articles to gain further understanding. If math and computer science do not interest you then Biomedical scientist might be more suitable since you don't need as much math but you do need more bio and chemistry. More specifically, for the hypothetical case of a biomedical engineer working on cardiac devices:

You get some data in a spreadsheet that tells you that your clients heart rate monitor is behaving strangely

you may work with MATLAB (or other computer programming) to analyze if it really Is having a problem or if it's a false positive. If it is a false positive you look at all the data sets to determine the root cause of the issue and implement a fix.

You go onto Wikipedia or pubmed.org to research more about the specific issue you face. You do statistical analysis on the dataset to see if the problem can be explained away using probability theory/statistics.
Sometime in the future you and your team fix the problem, maybe it's a revised algorithm that more correctly classifies arrhythmias based on the patient's heartbeat patterns, and you work a new project/keep improving efficiency and efficacy of your current project.
Like any other profession there are ups and downs, and the day to day will vary substantially based on your field an job position and company but biomedical engineering is a rapidly growing field and has a strong positive impact on society so it's a good field to get into if you're interested.