Should I trip alone?

So I bought a ten-strip of acid for me and my ladyfriend earlier today. She's out of town for the weekend so we'll have to save our little adventure for next weekend.

However, she's never done a psychedelic drug (other than weed) and I don't want her to have a bad trip or anything. I don't want to overwhelm her, so I want to take a tab tonight to see how strong it is so I'll know how much to give her.

Here's the kicker though: I've never did acid. I've tripped shrooms a couple of times (and loved it) but never acid. Also, if I tripped tonight I'd have to be alone in my room or outside alone. Should I go for it without a 'spotter?' Or should I just wait and guess how much to give my girlfriend?

EDIT: Two hours in I regret nothing. I feel fantastic. And now I know next time to take two or three and tell my girlfriend to take one or two. Thanks for the help everyone!