The mall is not located on Rt. 50. It is located on Rt. 13. From the location you've provided, you don't need to get on Old Ocean City Road at all. Go North on Old Hobbs Road and cross Old Ocean City Road (MD 346), to go onto Zion Church Road. Take this road to the stop sign and make a right onto Zion Road. Make a right onto Naylor Mill Road and then make a left onto S Mall Drive. You've arrived at the mall.
If you want to take highways to get to the mall, you can go South on Old Hobbs Road and make a right onto Rt 50. Don't leave the merge lane as you are going to immediately enter the Salisbury Bypass (Rt. 13). Take this road to the first exit you come to (Rt. 13 N to Dover) and exit right. Stay in the far right lane and enter the Northwest entrance to the mall.