I won't claim to be a rules expert. Certainly some on this form are more experienced than I. Anyway, there isn't quite enough information in your post to answer the question but I'll point a few things out:

1) Its now a 3 boat length circle. Length of the circle is defined by the first boat to get to the circle IIRC, so if a N20 gets there first the circle has a radius of 60' vs. 54' for a F18.

2) A proper race course has the gates separated by more than 6 boat lengths to avoid confusion.

3)) The rules are all defined based on how the overlap was established. If the starboard boat coming in last wasn't overlapped with any of the port boats prior to the mark round she MAY not have room. Not very likely to be the case.

Forcing a collision is always poor seamanship, no matter who has right of way. It is likely that the starboard boat had a rule 14 violation. Still, it is the responsibility of all parties involved to avoid the collision.