Hello @KATHLEENM379 ,
If your XLS or CSV file is that large from just ~300 contacts and 2 columns, I'm thinking there may be something else at play with your contact list, especially since we have customers that regularly upload files with tens of thousands of contacts without issue. I'd suggest either calling in, or replying to the automated @ mention email you receive from this reply, with the contact list in question so we can check it out.
It's also worth making sure that if you have multiple tabs on your file, that your contacts are only on the first tab. If you have any graphics or other elements in the file that'd be unnecessarily spiking its size, you'll want to make sure those are also removed. If this file is from another CRM, it's possible they included an "intro page" that includes these extra tabs and unneeded graphics.