I just prefer working in 1000ml, the answer is the same. Actually, it would be simpler to work in mL.
So if you wanted to get a concentration of 1ul/mL of n-propanol which is the same concentration as 100ul/100mL, you would add;
1/0.803 x 5.7 = 7.09ul. n-propanol
You will have noticed the answer is slightly wrong because you have increased the volume of the sample slightly but the answer is accurate enough in this case. If the volume of n-propanol was larger in proprtion to the volume of the sample, you would need to take it into account to prevent significant errors.