Working on my first schedule only rented room in condo from 9/1-12/31 Do I use expenses only for the 4 months?

Yes, that's correct.  Also, for annual expenses (like homeowner's insurance or property taxes) that may not have actually been paid in that 3-month period, it's appropriate to pro-rate them and list the 4-month proportion as an expense.  Careful, though, since you only rented a portion of your condo...  even those expenses from the 4-month period need to be prorated for the percentage of the condo that was considered to be rented out.  Can get a little complicated in calculating these.