Wait--
If Marriott exercised ROFR, then you could not submit a second offer. The unit would belong to Marriott. The way that ROFR works, if you submit an offer, and you and the seller agree, they have to run it by Marriott. If Marriott wants, it can then agree to purchase the unit at the price upon which you agreed. If it does, then it has exercised its ROFR, there has been offer and acceptance, and it will own the unit once it pays the price. If it does not exercise ROFR, then you become the owner once you pay.
There is no "exercise" of ROFR, then you get to submit a higher offer, and Marriott decides whether it will let you take it. Sounds to me like the seller/broker are running a little scam on you, using a phony exercise of ROFR to get you to pay more for the unit.