Can plan b fail ?

I had unprotected sex last night at 11pm

He came inside me by accident

So I took the plan b asap at 2am

I also took a ovulation test from cvs but a faint line appear guessing is negative

Can my plan be still fail?

I took a plan b last year 15 days after my period and it failed i end up pregnant but resulted as a 3 months miscarriage

I don’t want to have another miscarriage again

The difference between now it’s that is 12 days after my period that i had unprotected sex.