Am i doing something wrong when having sex with my girlfriend? i’m 17 and so is she

For reference I have never had sex before and she has had multiple times with her ex boyfriend before me so i’d be her 2nd time.

We tried having sex a couple weeks ago and while we was both aroused as I had done foreplay to her prior I just had genuine difficulty trying to get my penis in, it wasn’t like she wasn’t wet enough or whatever but i didn’t understand why as i know she has had sex before without this problem.

She wants to attempt at it again this weekend however this time she’s buying lube which i think will help but i’m also concerned it won’t so i was just wondering if there’s anything more i could be doing or maybe is it not my fault.

She did mention she may have a physical condition down there which could affect it which happened to her a couple months ago long after she had broken up with her ex so maybe that could be the case however i’m not sure and just worried because i don’t want her to be upset over not being able to have sex as she has been wanting to for some time