Well done! It sucks when different platforms can't get the data from each other, it's the biggest drawback for in my opinion, it needs a fitbit watch, afaik no other wearable works.
Garmin Connect is awesome! I only have a cycling computer from Garmin but when my Fitbit watch needs replacement, a Garmin would be the best choice to I have everything on one platform.
RE: Converting MyWhoosh FIT file to Garmin Connect