Convertible debt notes that convert at an unrealistic valuation

My company received a $15K investment from a friend of the family (we'll call him Doug) two years ago. I issued him a convertible note (no cap) that would convert to equity in either 2 years or if $1 million in additional funding was secured before then. We didn't receive $1 million in funding so the convertible note is now due to convert to equity on December 1st. When I initially made the agreement I got some bad advice from someone. Because of it, Doug's convertible note is going to convert to equity at a company valuation of $3 million. Because Doug was the first investor I also gave him an 8% yearly interest rate and a 20% discount on price per shares. My worry is that if and when we raise a round next year, the valuation is going to be MUCH lower then $3 million. I'm wondering how this would effect Doug's investment? Thank you.

If he's going to convert at $3m, but next year the valuation is lower, his investment will be worth less.

If he invested $15,000 at 8% interest with a 20% discount, that should be worth $21,870 at conversion.
(15000*(1.08^2))/.8 = 21870

At a $3,000,000 valuation, this converts to 0.729% of the company.
(21870 / 3000000) * 100 = 0.729

At this next round his percentage will get diluted based on how much you are giving out. If you are giving your next investors 20% total of the company, all current shareholders will be reduced by 20%. So his 0.729% would become 0.5832% of the new valuation.
0.729 * .8 = 0.5832

If you want to convert that back into dollars, multiply by your new valuation is. Let's say it's $1.5m, for illustration. Then his .5832% share in the company will now be worth $8748.
0.5832 * 1500000 = 8748

N.B. I just made up the 20% dilution and $1.5m new valuation as an example. Replace with actual values to get a more accurate answer.

Downrounds are pretty unfortunate for all shareholders, but such is the nature of investing.

Hope this helps.