You need to look at the other sales in your complex and neighborhood. 100 days may be 'normal'.
If other similar units are selling more quickly, try to figure out what about them was more attractive than your listing. Price is an obvious factor, but there are others to look at.
View? Colors not neutral? Unprofessional photos? Not enough photos? Is your agent actively marketing the property, or just letting it sit on the MLS waiting for a buyer? Are you having open houses at the same time the other units are open? I personally love doing Mega Open houses for condos and I make sure I'm the agent with the most signs and balloons to generate more traffic.
Video tours are great tools to market and post on social media. Are you posting on your social media? is your agent also posting the listing in every possible outlet?
Have your agent call the other agents who have sold units and ask them what they're doing and who they marketed to to get the buyers.
No need to give up, just make some tweaks and changes. I've attached a link to a booklet about assessing market value that may give you a bit more helpful info.
Best of luck!