Yeah, I agree that it appears to be incorrectly done from the get-go.
Ridgeline This is always a problem. Tension is the key as others have said. On A-Frame pitches ("Pup" tent pitches) this is always difficult. Attaching to trees always helps but there is always some you cannot get out. Your best bet is to drop one end for better water countrol. I only use one trekking pole and a found stick about 12-16" long for the "back". This will insure good run-off, good cross-ventilation, additional wind resistance and add some staking power to the rear. Of course, choose your ground so the water does not flow back under. MANY manufaturors do this with shaped tarps anyway. No reason you cannot do this with a flat one, is there? A tapered ridge line will also help "create" a bit of ventilation on still nights. Heat rising from your body will slide along the tarp in the direction of the highest point.
Staking looks to be off. Ideally, for good tension and holding, you want your stakes and guy lines along the diagonals. You don't seem to be close to this, but it could be the picture. Staking is MUCH facilitated by longer guy lines. The length of the guy line increases the leverage the stake has on the ground, hence tension on the tarp.
Of course, there are a lot of different pitches. Often, these are just sort of made-up as you go. I often use an ADK Lean-too type pitch with mine. This is just a lean to with a shorter roof segment over the front. Generally you need a couple loops at about 1/4-1/3 the length of the tarp, though. It stands about 6' high at the ridge and is easily heated with a fire. A partial lean-too uses about a quarter of each side to pull down as "wings; good for staking, wind resistance and will trap a bit more heat from any fire. A diamond is a good pitch for cooler weather with no fire; staked down on one corner then pulled tight over the pole at the diagonal. A minimal staking pitch(partial pyramid) is three stakes. A half pyramid requires 4 stakes. A Pup tent requires 6 stakes. And so on...