How to tell a girl I fucked up?

TLDR: I messed up with a three-month relationship because I failed to show a girl how I felt about her through physical actions, after she wanted me to escalate. How to tell her I fucked up?

I (32M) dated a 27F from late November through last Tuesday. She ended things becuase I fucked up, and I want to fix things and am looking for advice.

We never had sex, but I believe that she wanted to.

We texted a ton, conversations were always flowing, and dates were fun. I was slow to move romantically, giving a kiss on the cheek by the end of the second date, and only a quick make-out after dropping her off a month in. The next day, she went on a trip with her family for two weeks, and prior to leaving, we agreed that we wanted to see each other when she got back.

When she got back, she invited me over to her apartment to cook dinner for me and watch a movie. Her roommates were out of town. When we went to watch the movie, she brought a blanket and throughout the first 2/3rds of the movie, her legs were contorted around me in a variety of positions, but I didn't make a move. She ends up falling asleep halfway through. After the movie, she said she was tired, and I asked her if she was kicking me out, and she said no, because she didn't have anything to do early in the morning. I ask if I can kiss her, and we make out for a little. I back out first. I then say that she seems tired and tell her I'm leaving, but that I think she's great and am looking forward to continuing what we've started. She agrees. This is two months in.

Two days later, she texts me, saying that she was ending things because she didn't find the spark and romantic connection that she really wanted and was looking for. A week later, I text her, checking in. She's super friendly. I ask her to go on a run, and she writes, "I'd love to!☺️" We meet up for a run several days later, and I tell her that I feel like I did a terrible of job of explaining how I really felt about her. She said that things were moving very slowly, that that would have made a difference, and she had a hard time of telling where I stood or where my head was at. She says she'd agree to give it another go.

Texting is flirtatious and fun over the next few days. We go out on a Friday - I pick her up and give her flowers and a hat. We go inside her apartment at first to put them in water, and I probably should have made a move then. We go out for dinner, conversation is super good, and things felt good. She says that she wants to see where things go, because she doesn't want me to get hurt, but she does like and really care about me, and I'm fine with that. I drop her off, because she says that she has to go for a run early in the AM. We make out quickly outside, I back out first, and then I leave. We agree to get together next weekend, as we both have busy weeks.

Texting grows a little more infrequent over the next few days, but we still make plans to get together at a local parade the next Sunday. I end up seeing her spontaneously at a local bar, after doing a bad job of getting in touch with her. She's with her girl friends, dancing and having fun. i'm with other friends, so I stop by to talk to her a few times. I buy her a drink, which she seems super excited to get, but she's also had a few to drink throughout the day. After joking about my dancing skills for a little bit, with her showing me how to dance, I think that she says that she's going to hang out with her friends for a little. She comes by my friend group later but I don't do anything. I try to buy her another drink by last call, but she declines, which she later tells me is because she was in bed like a half hour later.

The next day, she texts me apologiizng for the lack of contact, bc she wasn't on her phone that much, and that she hopes I had fun. I text her to hang out, and then the next day she says that she doesn't want to lead me on bc she feels that her feelings haven't changed and she doesn' see this progressing. I politely wish her the best.

I am very attracted to this person, and I don't think she would have dealt with me for basically three months if she wasn't attracted to me, even the second time. I think that she's been looking for me to be more assertive, and other people have said as much.

I think that she ended up wondering what was going on. I don't it was the case that she never felt attraction or a connection or didn't see things progressing, just that I did not make any moves of my own.

How can I tell her and act assertively to let her know how I feel? She liked one of my posts on Strava recently. Again, I feel that there's still interest and attraction because she was willing to wait and deal with me, but I want to move forward.