With seller concessions it is the seller that is paying for the things that you listed that the concessions would cover i.e. closing costs. If you are buying the home for 280K plus 17K concessions the seller gets 280K for the house and gifts the 17K to your mortgage as per your agreement. You are purchasing the house for 297K and your mortgage is 297K over 30 years where if you had no concessions you would have mortgaged 280K over 30 years.
Were the concessions something you had to have from the seller so that you could get the mortgage or were you able to get the loan without the concession help? I run into a lot of people in MI that just don't have the up front money for buyer closing cost and have to ask for concessions. Dealing with this a lot I would also need to ask you if you think that the home will appraise for the purchase price with the concessions added on top of that, 297K? If not you could get half way to closing the deal and find out that the lender won't give you a loan because the home isn't worth that much.
If that actually happens, then you should seriously consider working with another lender/agent team who will make sure your interests are protected and you understand everything that's going on. I know it is hard because you're getting caught up in the excitement of buying your first home, but you simply must understand EVERYTHING. This is the largest financial investment of your life. You're likely financing for 30 years.... so you'll likely be living with this decision for a very long time. Understand it.