Likely within +/- 20%. The power reported by TrainerRoad will be within about +/- 10% and for most people the power on a trainer is generally lower than what they can produce outdoors.

If you want to know where you stand relative to other riders you'll need to start riding with others, initially on group rides, progressing to entry level racing once you have some experience riding in a group.

FTP is a measure of your 60min power which, as others have said, is not as important as your shorter term (1 and 5min) power for predicting how you'll do in a race. The easiest way to compare yourself would be to join a team or find a group ride that includes some racers. You'll know what you need to work on after you climb a few hills with racers who are working hard. If you live in an active cycling community you can also compare your Strava times on local hills with other racers. It's pretty simple to look up race results for the top 10-15 on a particular Strava segment. Stick with the hill segments (steeper the better) only and ignore the flat segments.