Hi there.
That initial excretion is popular coined the "pre-cum." I take it you were not using a condom for the beginning part of your sexual intercourse from what you're describing; before he put the condom on.
As far as I'm aware, yes there is a tiny tiny small chance that it can allow fertilisation to occur but it's very unlikely and you'd be ultimately unfortunate to ever become pregnant from the "pre-cum." Especially considering you used the morning after pill.
Which if you used correctly, should inhibit any fertilisation occurring from normal semen, let alone the pre-cum which is released in a smaller amount and with less concentration of sperm (as far as I'm aware.)
I would recommend resting your anxieties considering you have taken the morning after pill.
I hope this helps.