You didn't do anything wrong.  They just go through stages.  Mine did the exact same thing. The biggest thing is that you stay consistent.  The more inconsistent you get (or consistent with bad habits), the more she'll wake up.  First, make sure they really want to wake up and they are not just at the end of a sleep cycle and will go back to bed by themselves.  They do wake up, may cry a little and then go back to bed. This is were I went wrong with my first one... :-)  Then just repeat parts of their bedtime routine to make them go back to sleep if you know they are not hurting, have a poopy diaper, are too warm (feel if hands are clammy), etc.  What I do with my daughter is that I put her back down, give her the lovy and turn her mobile on. Then I walk out and wait a little while, even if she's crying (unless it's crying as if there is something wrong).   She'll settle down in a few minutes and the next night, she'll only cry for a minute without me having to go in.  Main thing, don't pick them up and out of bed unless something is wrong. Hope that helps.
Christine Wadleigh (nathan and abigail's mom)