3 person mechanic question

[DaveASA/FED]

I was 3rd baseumpire, person on 1 so I am in line with 2nd, hit to SS she throws to 2nd for force out, I watch ball till it nears fielder then focus on bag to see slide and fielders feet, I hear ball hit glove.....fielders feet miss bag, fielder comes down like no big deal, runner is getting up like no big deal so I give a safe call. So what is the issue??? Well I didnt' know till I started to move that the ball skipped off her mitt and was in center field!! So I feel stupid as I blew the "no ball-no call" theory. But even worse I start thinking what if she would have landed with her feet on the bag and I banged the out with the ball in the outfield??? Talk about crawlling off the field to hide!!

So I ask you what did I do wrong?? If I watched the ball longer I am afraid I would have missed the foot action, which in this case is meaningless but with a situation of a catch it is important......the only advice I have been given is I might have been too close to the play thus limiting my periferial (spelling) vision to see the ball skip into the outfield. One more thing is to get there, it had to go right over my head and I didn't even know it, now that is scary!!