You figure out you're closer to her face than to her crotch so you take the easy route and start descending the mountain you landed on. You try to not think about how nice it feels, even if the surface is slippery and sweaty there is something undeniably hot about what you're doing, even if it's your sister. You wonder if it must be something related to pheromones affecting you more at your size because you certainly don't desire to do any lewd stuff with her, you just want to explore a girl's body on the inside and she was the closest subject available. It still felt a bit weird though.
Your inner moral dilemmas about the scientific nature of what you were doing were promptly interrupted by an action that took you by surprise.
"I have to get ready then, see ya" Alice said as she hung up and quickly stood up, apparently she got a last minute activity for her weekend and she needed to prepare quickly. For you however it meant that the slow and introspective climb you were doing turned into a near death experience. As Alice stood upright you instantly went from climbing down to falling down, and because the surface was so slippery there was no chance whatsoever to grab into a tiny piece of her flesh and hang in there, you just started falling.
As Alice simply left without noticing the little bug that couldn't stick to her body, you prayed that the other part of the ring worked properly too, the part that would allow you to survive situations like this. The last rational thought you had was about having something to be able to stick your body on a surface just like bugs do, or else you would be at the mercy of whatever the giantess you wanted to explore happened to do like in this case. After that however you just saw your life passing by your eyes and got a rush of adrenaline and thrill from your body that almost wanted the impact to end your existence.
As it happened, you felt the weirdest thing, like you actually died for just a second before coming back unscathed, as if you just woke up there shrunken, in the grass of your garden. The experience was scarier than anything you have ever felt, but the ring worked! Your mission to get inside the body of your sister failed but you at least felt confident that you could survive now.
You tap the gem of your ring and grow back to normal, feeling a bit dizzy from the whole ride. You now wonder if you should persist with your sister and maybe tag along with her so you can explore one of her friends, or if you should switch your target. Maybe instead of being so sneaky about it you should just ask? Alice was not that interested in science but she liked adventure and fun experiences, and maybe getting inside her body sounded as fun for her as it does for you.
What happens next?