timing play in NCAA

[shipwreck]

Here is the stituation. Two outs, runners at first and second. Ball hit to centerfield. Girl on second heads for home and girl on first heads for third. Throw comes in towards home but is cut off by the pitcher who fires the ball to third and they tag out the runner at third BEFORE the runner slides into home. I am PU and set up slightly outside the right handed batter's box for a possible play at home. I see the tag at third, have time to look towards home and see the girl hasn't made it to home at the time of the tag. I verbalize loudly that the run doesn't count while giving a strong safe signal. After the game when I was talked to about my performance, I was told I should have been set up on third baseline extended which would have lined everything up perfectly for this call and it would have been an easier sell. I can see this, but is that a good place to be if the pitcher hadn't cut the ball and the play was at home? Dave