Is it even possible I am the father?

Off birth control 10/8/11
Irregular periods
She says no period in November
LMP 12/18/11
Together 1/4/12-1/6/12
Vaginal mucous present during that time
No birth control from me(intercourse 8-9x)/removal method from him(intercourse 2-3x a month)

1st u.s. 3/14/12
U.S. GA 7w 4d GA 12w 3d Due Date 10/27/12

2nd u.s. 3/23/12
U.S. GA 9w 3d Due Date 10/23/12

3rd u.s. 4/20/12
U.S. GA 13w 0d Due Date 10/26/12

Had u.s. on June 1st, I believe the due date has stayed the same since the April u.s.
Based on conception/due date calculator. Conception occurred 2/3/12
28 days from when we were last together
We are both smaller people in stature

I just want to know if there is even any point in getting a dna test done. To me right now I am not the father based on my research but if there is still a chance I am the father, even a 1% chance, then i still want to know for sure. Thank you for your time.