First deselect 'Match Sequence Settings' if it's ticked.
In your export window (just under 'Match Sequence Settings') choose H.264 from the 'Format' drop down menu.
Then choose 'Match Source - High Bitrate' from the Preset drop down menu.
At this setting your 28 minute programs will be around 2.2GB in size when exporting is finished.
If you want smaller then choose 'Match Source - Medium Bitrate' from the Preset drop down menu in your export window. This might give you about 600-700MB file size for a 28 minute program.
Keep in mind as Neil has mentioned the smaller the final file size the more quality loss. However if you only have a fairly simple video without fast action, lot's of cuts or complex images, you may not see much quality loss.
If you want to delve into 'datarates; when exporting and experiment with your own, scroll down further in the Export Window and look for the 'Video' tab - select it, then scroll down until you see 'Bitrate Settings' - this is where you can change settings to higher or lower datarates if you don't want to use the presets..
The two presets mentioned above if you look at their 'Bitrate Settings' for 'Match Source- High Bitrate' is 10Mbps and for 'Match Source Medium Bitrate' is 3Mbps. So a 3Mbps export is going to be about the 3rd of the file size of the 10Mbps export.
Sounds complicated and it does take getting used too. But keep in mind once you have a export setting you like you can save it as your own preset. Or just use the existing Presets. If you look at the Presets list for H.264 you see a whole bunch to choose from.