Don't feel bad at all. Take me for an example, i'm one of those people who does everything-netball, drama, theatre dancing, softball, swimming, everything. Then last year I got really sick which meant I had to drop pretty much everything but drama. My bf does not think i'm boring though at all. He loves me for who I am, not what I do.
If this girl, is any kind of nice person, she'll understand and care.
Try doing other things if your getting bored though-like learn a language, or take a class in something non physical. but only do it for you, not anybody else.