Why am I (21M) scared of committing to the girl (20F) that I actually do quite like even though this is what I have initially wanted?

Let me just give some essential info briefly to give some context.

I have been in a couple of relationships, only one of which was serious and long term (nearly two years), however, I wouldn't really say I have ever fallen in love before. This girl I have been seeing is quite special, and would say is deeply in love with me. I do quite fancy her back too, I sometimes feel like I actually do love her like no other girl I have ever loved. However, I can never bring my mind to commit, even though that has never been a problem for me in the past and was my goal when I was dating her. And now that she is mentioning it and asking me if we are boyfriend and girlfriend, I keep kinda running away from the question – while I don't even know why.

I do like pretty much everything about her, except a couple of things, some are fixable some are not – either way, I am fine and want her as she is.. I genuinely am deeply in love with her, and I hate this feeling of not wanting to commit and being scared of falling for her and putting on the label officially, as if I would miss out on things (or other girls) otherwise – sounds really nasty I know..
I could have easily said yes when she asked if we are officially together and I wouldn't have lost anything, but with this one relationship, I don't wanna be rushing anything and wanna make sure that nothing is forced. And apparently, I cannot get myself to actually be official with her unless I feel like I am forcing myself, even though I actually have deep deep feelings for her.

Has anyone experienced something similar to this before? Does anyone have any explanation for this? It's a gutting feeling not being able to easily fall in love even when you finally do want to.

TL;DR Cannot get myself to feel comfortable enough to fully commit to someone that I love and loves me back.