I can't record the whole field, what should I do?

The field of view from the phone camera is determined from the distance of the plate to the fence.  There will be times where you get complete coverage from 1st to 3rd, and times where you will need to make a decision on what to capture.  

This is the recommended position, it to capture the 1st base side.

This is an example of 3rd being covered, vs 1st, and not recommended.