My (21f) girlfriend (22m) subtly said she wanted to take a bath with me and I didn't want to. Am I the ahole here?

I have occasionally asked my girlfriend if she wanted to take a bath with me over the past few months and she has pretty much always declined. Tonight, I was planning on taking my bath as I do pretty much most nights when I just want to unwind and relax. She subtly asked if she could get in the bath with me and I kind of groaned and dismissed it by asking if we both could fit in the tub (this is a new home and bathtub than the last time we took a bath together). I believe she thinks I declined because I didn't want to see her body. She gave birth to our child around a month and a half ago and I've tried to reassure her that I love her body. Maybe I'm not doing a great job at that and that's where this fight stemmed from. In my mind, I simply wanted to get a bath and relax. I guess I just wasn't in the mood for a couple's bath tonight. My partner did not take it that way. I just want an outside perspective. Thanks

TL:DR - I didn't want to get a couple's bath with my partner tonight even though I'm usually the one who asks and it turned into a fight.