Do you have a finance spreadsheet set up? We found that really useful to see which categories we spend on and what can be cut down or set a budget for. Same with meal planning and food shop budget
Providing that you aren't left with very little after bills you should be OK, and that is relative I know but many make it work no matter how little they have each month.
If you price up nappies and formula (if you intend to use or if you end up needing to use it) and add that in to your outgoings you'll get an idea.
Then you can factor in wipes if using, weaning, baby groups etc.
You can use reusable nappies, second hand or a starter bundle upfront then low cost, you can use water or oil to clean instead of wipes, you can get everything 2nd hand or gifted other than mattress and car seat (maybe family can chip in?) babies need very little and each month especially if breast feeding it won't be a huge amount more during the first year or two.
Bottle feeding you can buy mam bottles which self sterilise in the microwave saving money on a seperate steriliser.
Weaning wise, baby led is pretty much what you eat so cheap, or purees are obviously cheapest if made yourself not bought in jars or pouches so maybe add £10 worth or less per weekly food shop for when they are eating.
We had dd when I was at uni and dh just left uni. His pay was lower and rent was higher than our mortgage is now and we had very little to no savings and we got by just fine. Dd had lovely clothes gifted or 2nd hand off ebay or nct sales. Pram was 2nd hand off ebay (we bought a new SX pioneer when she was almost 2 to suit needs and when money came in)
If your disposable income you mentioned is post any payments or subscriptions then you will be more than fine!
try not to let the stress overwhelm you. We have enough anxiety in pregnancy as it is!