Dude, it sounds like a great start to progressing your game if she was willing to do one better for you in giving you the number. Thats a IOI right there. With regards to getting her back to your house after you have had a few drinks on your date here are a few suggestions:
1. As you are leaving after pre-drinks show her the Hot-tub. Dont do it before or give her a tour. Do it like a last minute thing and just say.. oh before we go come check out my Hot tub. Show her then say we should fire that baby up after drinks and wait for a response.
2. After you have your drinks and are having a good time just say midway through. I am bored being out, am gonna go back and get into the Hot tub and you are welcome to join me.
3. Dont show her the hot tub when she arrives for pre-drinks.. go out have fun then just be like "did I show you my hot tub".. she'll hopefully say "no, you have a hot tub"? and you can say.. yes, we should so get back and have a night cap and you can see it in the process.
Just ideas.. add improvisation, whit and charm
