I live in a flat area but my races is in a hilly area? Is that a problem?

No.   Number one priority is cardiovascular fitness.

• That said - for optimal race preparedness you should try to also put some heightmeters in your schedule (in an ideal world some sessions with same height meters per 10km as in your race situation).
• At home - UTC will try to help out finding elevation change in your area by suggesting hills to train on (see also Hill Finder).
• And you may want to organize some Weekend Chocs in areas where you can do longer ascents and descents.