Okay, so let's just ignore for a moment that the Marvel universe has freaking metal manipulators like Magneto and Polaris, who would absolutely wreck your shit, like Wolverine and Colossus would attest. Let's consider the physics here.

This is from some quick and dirty searching online: steel has a melting point of about 1500 °C. For comparison, a meteor heats up to about 1600 °C and its slowest speed is about 34 machs. Unless your character has some way of mitigating heat caused by air friction then you can only run or fly at about 15% of your maximum speed before melting into slag.

So I would say, yes, you are overpowered in the sense that your own powers would kill you.

Creative Commons drawing of a Rust Monster from the original DND monster manual (not marvel canon)

I’d say the flight and speed make you overpowered.

By "my skin can fully turn into steel", do you mean exclusively your skin?

Skin isn't very thick and most of the sources I'm seeing wouldn't put it much thicker than 3mm at some of the thickest points with a generous definition of "skin". I'm seeing that you'd need about 13mm of steel to stop shots from most weaker handgun and rifle depending on many factors. Considering you'd need at least four times more steel than what you'd find exclusively on the soles of your feet to stop smaller/slower bullets I find it hard to believe that skin deep steel alone would make you completely bullet proof.

Supposing the steel did stop a bullet, though, the force from the impact is still going to hit you and likely cause some bruising to everything underneath the steel. Bulletproof vests slow bullets down before impact and distribute the load, but skill cause bruising. Raw, unshaped steel will offer no such benefits so you'll have the same (large) amount of force being applied to a smaller area on your body more suddenly.