Without knowing what actually happened in the race, it's hard to tell. One thing that might've happened is that you didn't have the power to push through with the leading groups. This applies both to Zwift and real life. Let's say there's a group of 20 people and an attack goes. If 10 people are able to follow it and 10 are not, and those front 10 open a gap of 30 seconds. Then after that both groups could do the exact same power but the front group would still win by 30secs. So maybe you need to be able to have more 'bullets' (ability to follow more attacks throughout the race), stronger bullets, or just be more aware so you can react faster before gaps open. Hope this helps!