HR training

I'm new to a HR program and using a HR monitor.  Today I did a bike training and was supposed to stay in zone 3, I had trouble staying in the range, so I turned off the alert for the max range.  Any suggestions on how to stay in range?  Also, is it bad to be too high?  I know it's not good to be too low because I would not be working hard enough but not sure if it's bad to be training in a higher than recommended range or at least going over the range sometimes.

Thanks,

Bill