it's incredible how many times i've loaded my moto by myself onto a truck bed/back of van using inappropriate equipment.
making a foldable ramp was your first mistake. why are you messing with hinges? you're just asking for them to fail.
all you need is to find an appropriately angled driveway that you can park your truck against. the ideal situation would be a driveway angled down with the street angled up away from it, making a mild V. that will effectively lower the height of your truck's tailgate as well as shorten the necessary length of the ramp. just use one piece of wood to bridge the gap. i've loaded a very heavy '71 Honda CB500 into the back of a pickup truck this way by myself. it's stupid and i don't recommend it, but it will work better than what you're trying to do.
whatever yo do, don't film it and put it on youtube.