Hi Jessica,
Thanks for uploading your shapefile. After a quick glance, it appears that this data has a lot of vertices for the polygons, 3591158 vertices for one feature and and 3189855 for the other. The following blog mentions some considerations when working with data with too many vertices and strategies to reduce this:
Dicing Godzillas (features with too many vertices) | ArcGIS Blog
Please try reducing the amount of vertices and then re-adding and publishing the data.
Please let me know if you have any questions,
Kelly