I did some mall approaches a bit ago, and I usually find that if it's a completely cold approach, chances of success are low to none (at least for me, and I'm not that good). However, if you are getting IOIs from her before you open the convo, go in there.
I just happen to look good in a tight shirt, so when I go out, I wear it. It gets me noticed, increasing her IL and giving me a better fighting chance. So do something that would get the HB's attention.
Your line seems too formal. Personally, I don't like the "excuse me". You don't need to be excused. After all if shes giving you IOIs, it is SHE who wants to meet you!
Try to notice something about her, and comment on it. Just be prepared to provide 90% of the conversation, initially. Don't expect a 50-50, like you would with a friend.