As bikerboy says, it needs to be cleaned up. The poor performance you felt (many people call it "sputtering") is from the oil getting into the spark plug wells. Walmart should remove the plugs to clean them and the wells and should clean the engine compartment, then replace the lost oil. No need for you to miss work; it is okay to drive as long as you keep an eye on the oil level. It would be very unusual for the level to get dangerously low from a missing oil cap - I have gone weeks without noticing the cap was missing and was less than a quart down.

I'd worry more about if anything was damaged inside the engine from it running with the oil level dropping consistently over the span of days than I'd worry about the oil doing any damage outside the engine.

As for what to do with Walmart, go explain to them what they did and ask them how they're going to make it right. You might also want to take the car to a mechanic before going to Walmart to get an estimate on how much it's going to cost to fix the damage and to figure out how much damage was actually caused by what they did. From there it's up to you to decide what you settle for or try to make them do for you. Good luck

check you oil, if its stll up on the stick, you are probably ok damage wise. You are lucky oil is not dripping off the inside of your hood. Only thing to do is clean it up.As far as walmart goes, you wont be able to prove they left the cap off after griving a week. ALWAYS check things over after a service before you leave the shop. Lesson learned.

oil splattering over the coil leads and down the plug holes would cause a miss-fire. needs cleaning.

Your timing seemed off? What?

Got an oil change on tuesday. Drove till friday. Stayed at home all weekend. Monday morning my timing seemed off like a spark plug wasn't firing or something. So I pulled over and looks like walmart never put the cap back on my engine where the oil goes. Looks like it leaked around my spark plugs and might have messed them up. What kind of damage could be done and what kind of compensation can I expect from walmart. Losing money by not being at work :/