Am I spending too much/ saving enough?

Thanks for coming to my post. I am a PhD student in the UK and want some investment advice!

Income: PhD stipend £1470, teaching tutorial classes twice per week: £100 - £200 depending on class schedule, so let's say £150 here, that will be £1620 / month. Good thing is I do not get taxed at all for my income as a student.

Breakdown of my expense Rent + bills (living in a LCOL city)= £500 Transport = £50 Food + entertainment = £500 Others (clothes etc) = £200 so that will be £1250 so say £1300 per month. This will allow me to save around £300 a month.

I am now 25 and prior to doing my PhD I have worked for a year (and another year as part of my undergrad studies) and have saved £10k in stocks and £9k in my Lifetime ISA (including government bonuses).

Do you guys think I am saving the right amount given my low income? I am planning to put my monthly savings in some UK/S&P ETFs. What do you think?