Is it bad to steep tea for too long? would i gain more egcg catechins if i steeped longer?

Possibly: You might ingest more catechins the more tea that is actually infused into what you are drinking (is it green tea?).A 90-day study in Food Chemistry Toxicology from June 2008 studied males and females who drank green tea daily and saw that only 5% of both sexes had elevated liver enzymes by the end and neither showed cellular changes in the liver. This may need more investigation.

To be honest: Steeping times really just contribute to the "strength" of taste. If you let tea sit too long, the "antioxidant" value decreases as it's exposed to oxygen and oxidizes. But I wouldn't worry about it too much, just try to drink it within an hour or less.

No: Not dangerous, just may make taste stronger / more bitter.