Not exactly sure what you mean by an extra line adding in the box 3 $$ again.
Guessing:
On the PART 1 list of interest items on the actual Federal Sched B?
IF so, that Extra $$ amount might be coming from box 8 on a 1099-OID....if you have one. Those $$ are separate $$/items that add to the list of entries on the Federal Sched B.
...but the box 3 $$ should only show up once for that particular payer (but added to any box 1 $$) On the Sched B...unless you somehow happened to create two separate 1099-INT forms and repeated the box 3 entry by itself.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
