@Joseph Parker, I'm not a lawyer, this is just my 2 cents worth, but if you didn't turn in the EM on time, then the seller may be justified in backing out of the contract. You may have a case because the agent told you no rush, but then again, it could be referred back to the contract that said it needed to be submitted by a certain time frame, regardless of what the agent told you. In general it wouldn't of been a problem that you didn't turn in the EM until Monday, except in this exact situation where the seller got another offer and wants to take it.
If you're not interested in working with the seller any longer and would prefer to walk away, then you can chalk this up to a lesson learned and remember to turn in earnest money ASAP in the future. From my understanding when I was an agent, you do not have an executed contract until all parties have signed AND the EM has been submitted. I would also keep that in mind for anything else in your purchase agreements, to always keep to the deadlines and if they change at all, to get an amendment to the original agreement, just in case an agent's email agreeing to the change isn't accepted by a court, should you ever decide to go that route.
Good luck with whichever way you decide to go!