-Convertible debt notes already come with a (low) interest rate.
-It's pretty clear the reason you are getting such bad terms is because you have no leverage in the negotiation. You've made it clear that your company desperately needs the money; the investor probably knows you're desperate and that's why you get such bad terms. There is a lot of truth to the saying that it's best to raise money when you don't need it: because then you can afford to walk away from the deal or spend more time finding other offers. Firstly, try to negotiate better terms. When someone presents a term sheet to you, it's meant to be the beginning of a longer discussion. Ask for a $4MM cap at 25% discount, and work your way down from there if you are refused. While that's happening you need to explore other options: 1) Find a better offer (get competing offers), 2) Position your company in such a way that you can afford to go without funding (firing people, cutting expensive programs), 3) If you're desperate you'll have to bite the bullet and take the deal.
-Keep in mind that if you don't get better offers and can't negotiate a better offer, and if there is absolutely no way your company can survive without funding, then obviously you need the funding.
-I'm not able to refer you to a lawyer, but keep in mind that you should involve a lawyer in the negotiation. Your friend probably knows more.
Other points:
-Why the hell do you have 8 full-time employees? How are you paying them? How can you justify that expense? What kind of business are you running that has such a high burn rate?
-Can you raise money from non-traditional sources such as family & friends?
-Are you actually truly pre-revenue (as in negligible revenue)? If so, that again begs the question as to why you even have 8 employees and expensive marketing referral programs. Those are not things you do without already having lots of funding.
-Since you're "pre-revenue," why do you even think you've found product-market fit? Is it your daily active users number or monthly actives?
-I wouldn't consider a $250k exit a "proven track record of building and exiting companies." Though it is a positive for investors, I don't think investors would consider it a proven track record.