I think the keys to pulling off this style are fashion, body, hair, and makeup. I would start by doing some research on what makes an outfit "bombshell" to you. In my mind, this typically constitutes low-cut dresses with heels, tights, etc., but Pinterest will be your best friend. Don't forget about accessories either. Having a nice bag and modest jewelry (thin gold/silver chains, pearls) that can go with any outfit will really elevate your look and keep you from looking trashy or cheap. Also, when buying clothes, don't settle for anything that "kinda fits" or doesn't look good at you. If anything is off and you don't plan to take it to a seamstress or tailor it yourself, then don't buy it. It'll just sit in your closet and burn a hole in your wallet.
This leads into another important part, which is going to be your body. One of the hallmarks of bombshells are their curves, so if you aren't toned already, that's something you'll need to get started on, but having a little fat on top (within a healthy BMI range) is something that is also compatible with this style. Although you can weightlift for stronger curves from the side, there really isn't much you can do about a high waist-to-hip ratio (regardless of what people on the internet claim). If you're someone who lacks a defined waist, shapewear will make a difference (corsets, hip pads, etc.). For the bust, investing in a nice push-up bra should be enough.
As for hair and makeup, it usually has a very bold style. You should look into and start practicing blowouts for bouncy, voluminous hair. For makeup you'd want a strong lip color, thick lashes (but not too thick, keep it as natural yet flattering as possible), and defined yet feminine brows. It's also worth mentioning that there is no definitive blush and contour placement for any style. This would depend solely on your face shape, and you should pick what placement flatters your face the most.
Most importantly, to top it all off, you're going to want to work on your personality. From your post alone, it sounds like you lack confidence, which is something that just about every bombshell has in common. I struggle with this myself, so although I cannot offer any specific tips, just know that this will probably be your biggest obstacle. You also mentioned you were worried about not being attractive enough to pull off this look. I'd like to take a moment to point out that (although this may come off a little rude) Ana de Armas is honestly not that attractive if you look her up in plain clothes without makeup. However, her appearance and demeanor clearly stand out to you when she is all done up. Use this as your inspiration. Fashion, hair, makeup, and personality can take you a long way.