The Market everywhere is tight. 20% gross margin isn't going to be enough to move the needle on a 120k sale. If you are using hard money and you get a deal on the listing, say 3.5% commissions total, 8-9% of your gross is eaten by closing costs both transactions, commissions and holding costs if you hold for 4 months or less, figure 7% if you don't use hard money. The other thing people forget about is concessions, on average at that price point consider 4k in concessions because thats FHA / VA buyer all day long and they need the cash back to pay their side of the closing.
120k purchase x 7% = 8.4k
120 - 8.4 - 4 - 40 - 56 = 11.6 profit
If you go over on your buy, make a mistake on repair estimates which its alway 3-4k more than what you think, Or have to sell for anything less than calculated ARV, what's left?
You need a larger sale price or ways to reduce costs. If you use hard money you are looking at 9k profit if you were perfect on estimates and sale price etc.
Other options are to start looking off market, network with other investors, market for deals.