The equation you are using is correct. The first thing I would say to check is your units (because you did not show your actual work, or steps, I can only guess).
The reason I say so is, because you said the answer should be 4884J, enthalpy is usually given in kJ.
So the question is, what are you using for R and what are the units of R?
Do they cancel properly? Are you using the correct R that will work with liters and atm, or did you convert those units?