Report Builder - 3rd table doesn't return multiple rows

Please be gentle, I'm a newbie!

I have written my first report, (Nav2013 SQL db) it's quite a simple report but I must have missed something because the results are not quite as I expected.

I have 3 tables in the report:
Service Item (Fields: Serial No., Customer No., Warranty End Date(Labor)
Customer (Name)
Service Contract Line (Contract No., Contract End Date)

All is fine PROVIDED there is only ONE contract PER service item, however there are often multiple contracts with newer dates and I either must show all the contracts or just the latest contract expiration date.

I can change the report to use the Service Contract Line table as the base table, but then not every Service Item has a contract, so this won't work either.

How can I do this?