Dude, if you're getting a bunch of IOI's, it's time to cut the crap and give her an SOI. Let her know you're interested. When you planned to go on a walk and someone else decided to come with, you should have said something like:
"Haha, come if you want, but it might be pretty boring... I know I don't like being a third wheel

"
Or something about how it might be awkward for them because this girl is gonna be all over you. Let them know in a fun way that you want to be alone with this girl. If she likes you, there should be no problem.
Or when she asked you about girls you like or whatever. Say something like "well I'm TOTALLY in love with this girl. she's really cute... blah blah blah (start describing her)...I don't even care that she's totally lame

"
If you never take the shot, you'll never score
