When my cat was 23 lbs, I ended up buying a bigger carrier. He's now 14 lbs and I still carry him in that huge thing because the smaller one is for 12lbs or less & he still won't fit. The size of your carrier may be some of the issue.
My cats never really enjoyed getting in those things, and they would pretend they were going to fight me. Really though, I just picked them up and put them in without much issue. I would have the carrier out of their sight at a reasonable safe height with the door open, and I'd pick them up the way I normally did if I were just planning on holding/petting them (pretty much distracting as I walked to carrier). In they went and door shut behind them. Of course you have to have a cat that allows you to hold them that way, and I know not all of them are like that.
EDIT....just realized there were 2 more pages of responses. OOPS! Maybe useful info for the future. LOL