Track 400 meter time?

So we had a track meet this morning and I ran the Sprint Medley Relay. The sequence was 100m, 100m, 200m, and then the 400m which I ran. I don't exactly know what my time was but it was probably around 1:10-1:15. When I was running I caught up to the first place runner at the 100m mark and kept neck & neck with her until the 300 and then she started sprinting and I kind of died out slowly. I felt pretty bad about not keeping up with her till the end and I run the 400m individual race usually. Anyways do you guys have any suggestions on helping endurance/stamina and my 400m time? Thanks in advance!