You may have prefect form, I don't know. When you say it's hard to stand up, why is that? Just that you're gassed, or does your back hurt? If it's back pain/tightness, I'd definitely check my form. If not, maybe you're fine. Either way, I think you can do as many reps as you want as long as you maintain very good form for all your reps. I know I used to do too many reps on DL and would let my form get sloppy just so I could finish my sets or set a new rep record. I'm done with that. Form is paramount.