i am by no means an expert on such matters but personally - i mix my running up with resistance/weight training twice a week - i go to a body pump class, and i do find that when i stick with the class as well as the running, i notice much more of a difference to my overall muscle tone.
you cant spot reduce fat on your body - you have to reduce it all over and for a lot of people, me included, it seems to stay for longer around the middle and is harder to shift! again i am not a dietician and this is what works for me but i would suggest making sure you are drinking a lot of water, perhaps reducing bloating foods like white bread/pasta and swapping for brown, eat plenty of fibre and veg/lean protein and do some planking!!! my evil body pump teacher makes us do what feel like hours of planking while moving up onto hands and back down onto elbows repeatedly, moving feet in and out while planking and then doing the one where you bring your legs up to the side of you while planking as if you are climbing. its a killer. but seems to work! 
oh also - try not to eat more than you need - marathon training makes me want to eat the whole chocolate section of my local shop!!
congrats on the weighloss and first race RFF - i hope you enjoyed it!