Making a gif for twitter in After Effects - file too big!

Hi,

Photoshop will be a better option to export gifs. Import your video to photoshop and in file menu, select save for web option.

Under that, export as animated gif. You will have more control on removing unwanted colours, selecting different form of gif compression and you can have alive preview of the gif before exporting with an approximate file size too. if you can make the video in less number of frames per second, the number of frames for animation in gif will also reduce accordingly.  Or else, you have to go with some online gif converters from mp4

Filesize is hugely dependent on duration and resolution. How long is your video?
I will also set the height to a number divisible by 4 as this is a MUST for the majority of compression algorithms.

Lastly, look at using MP4s for Twitter as you will be allowed to tweet videos with a max duration of 2mins and 20 seconds.
Another option is to post an external video link in your tweet. HTH.