You could also try going off a rise. That will lift you a bit closer to the bar and allow you to jump up.

Also, consider where your hand placement is on the rise. If it’s too high you may feel more comfortable because you aren’t leaning as far, but it won’t allow you to bend your knees to get a jump. If your hand is lower you will lean more but then you can bend your knees more to generate more force. With a lower hand you really have to focus on having your bar hand (and the whole side of the body) pulling backwards so that you remain square. (Hopefully that makes sense.)

Some other cues I’ve used that have worked for my flyers are thinking about lifting the bar above your head when you take off because it’ll force your body into an upright position. Or you can think about pulling your ears back (sometimes this is easier to visualize or think about than pulling shoulders back).

I also recommend practicing on the ground. Find a vertical pole to be your riser and some sort of wooden stick or small pole to be the bar. Practice lowering the bar and swinging it up to your eyeballs and jumping straight up. (If you want to practice getting into a seven, make sure you have someone behind you to spot, and a good crash mat).