what are your timeline settings? if you are just going to >file >export, where it just starts going, it will export the sequence in its current format, which most of the times, will be a prores422 codec and it will come out uncompressed. if you want to compress it as you export it, you can go to >file >export with quicktime conversion, and select something like a h.264 codec for online stuff, set the resolution and other settings how you want and it should come out in the 3-5 hundred Mb range
and to the OP, make sure you don't accidentally have a clip selected when you go to export or make sure you don't have in and out points set on the timeline for some reason. those can eff it up too. and yeah get rid of the markers on the timeline itself, not the clips, if you don't need them cuz i know those can possibly affect it too
