The last two days I've had a very nice young guy here from Kentucky. Pretty good caster himself, with the usual minor problems with subtle creep, some hitches in how he accelerated the rod, and short, ineffective hauls. Great progress was made. He threw pretty nice loops, but didn't get the line as straight as I like. Both his rods were quite fast and he struggled with that a bit. Fast rods require that the line be very straight to work as designed. He had never tried using any line on either rod that wasn't the weight the rod said it wanted. I suggested we go up a line weight on each rod, it was an eye opener for him. The bit of extra weight made a huge difference in how the rods worked for him, he liked both rods much better and cast better as a result.
I've run into this many times over the years, anglers reluctant to try different lines on rods, some even think they will damage their rods by using a heavier line than the rod is rated for. I've put 12 wt. lines on 3 wt. rods. That did make the rod extremely slow, but it did cast just fine... And I once had a 9' 4 wt. rod that was very unpleasant..... A group of us tried various lines on the rod trying to make it useable... Going lighter made it worse, we finally all agreed that the rod was best with a WF-8 line. The rod was a very nice, slow 8 wt!
So, don't hesitate to try different lines on any rod, but especially those that just don't feel "right"... And no, you won't hurt your rods!