First of all, I hope you are feeling OK.
I had a biopsy earlier this year and flew about 10 days afterwards. Consultant didn't seem to think there would be an issue. I have flown five times since then and will be doing so later this week (just getting a load of holidays in before my brachytherapy/radiotherapy next month).
I suppose in your case, the fact that there are only 3 or 4 days between your biopsy and flight is the main worry. Did you ask anybody at the hospital about it? Might be worth asking your GP.
Based on my experience, but obviously please don't take this as medical advice, If everything seems OK with your waterworks, I guess you should be fine.
Just make sure that your travel insurance company know about your medical procedure and any likely follow ups. I currently take out a short-term policy with Admiral every time I have a holiday.
Best of luck with everything going forward.