to be fair gravel is not dirt and even though I am able to handle myself on a dirt bike, I still get nervous sometimes on a gravel road with the wrong tires. You will get the hang of it, don't worry it will come with seat time. I recall the first time I tried dirt riding, my friend brought me to a riding spot with sand trails and whoops. I nearly shat myself. Now I can hit whoops at unreasonable speeds with the bike kicking and crossed up thinking "this used to be so difficult!"
What really helped with my dirt riding is just finding an empty field and practicing turns, stops and starts. It's a strange feeling turning the bike underneath you and pushing it into the ground vs the usual street riding style of shifting your weight to the inside. But you will be surprised how much grip you can get in the dirt. Just beware this doesn't translate to slippery gravel roads.
Also regarding standing up, the key is to keep yourself centered on the bike and clamp the bike with your knees, slightly bent. Hands always relaxed on the controls or you will get arm pump. In this position you can ride over nearly anything and not come off the bike.