I know this is an old post but as I have a similar issue to calculate, so I thought I would put my two cents in. Did you take into account the loss/retention of medical (and other) knowledge into account?
For instance the first generation or two will still have 'modern' or ' future' day medical knowledge even if they do run out of medical supplies/technology. So at first there could be a slighter higher birth and survival rate than expected! This knowledge can then be lost over succeeding generations resulting in a decrease in birth and survival rates back to say 19th century Industrial Revolution equivalent and then even worsening to Medieval growth rates if you are particularly vindictive to your population.
Assuming that women accept their lot as broodmares for the survival of the community; You could work on the fact that women can survive an estimated 3 births (using similar reasons you used for 2) for a generation or two. Giving you a starting population of, um...hang on.
If you have a starting population of 2000 and assuming equal male to female ratio like you have you get 1000 a piece! You then have to take into account any older women or younger children who are not of child bearing age! Physically not possible! So for arguments sake you cut it 50/50 again, so you have roughly 250 old people, 250 kids and you get 500 women of childbearing age who have roughly 3 kids each over their lifespan. That's 1500 in the first generation (not taking into account any multiple births - apparently there are 32 twin sets per 1000 births).
For the second generation: You have two scenarios. If your starting population was mostly adults to start with you would have a large age gap between your first and second generation with a potentially large loss of knowledge etc occurring. If you had a normal demographic of young, adult and older people in your starting population you would have a more even retention of knowledge over time.
I'm using the even demographic scenario here for generation 2. These would be the ~250 kids who were born off planet and presumably had a good start in life health wise. So they would be robust, maybe having some medical procedures at birth making them more healthy than those born on planet. Let's be generous and say they get the 3 to 2 birth rate mentioned above. So 250/2 (male to female ratio) = 125 grown teenagers/20 something's ready for childbirth around 10-15 years after landing. That's roughly 250-375 more babies bums to wipe. Let's say 300 for the sake of easy numbers.
The third generation would be the children of your 1500 initial births. So, 1500/2 = 750 girls reading for childbirth 15-25 years after landing. Unfortunately for them, they have a higher chance of all those childbearing issues mentioned above so say only get the rate of 2 births per female. 750*2= back to 1500.
So after 25 years, you have gained:
an initial population of 2000
First generation born on planet of ~1500 (fairly healthy infants - benefits of pre landing technology and tech)
Second generation born on planet ~300 (fairly healthy infants - benefits of pre landing knowledge and maybe some tech)
Third generation born on planet of ~1500 (starting to increase infant mortality - no to little pre landing tech and starting to lose knowledge)
That's 5300 people not including any losses, and that is optimistic! Let's say a third die to disease/predators/conflict/human stupidity. That's only ~3500 in 25 years. That's a fairly high growth rate of 1.75% (between 1950-2000AD we had a growth rate of 1.7%). It's from here that you could possibly have a level or downward rate to calculate your population over the next 75 years.
This older similar question may help especially the first answer with growth rates provided by the Real Population Problem
Factoring in the knowledge base of where your population comes from and the loss of tech and supplies I think we could adequately place them in the 1870 - 1950 AD era for the majority of the 100 years but for the first 25 I would say use the 1950 - 2000 AD growth rate (which pretty much lines up with my calculation above!)
•25 years at 1950 AD to 2000 AD rate of growth at 1.7%: 2000×1.017^25≈3048.
•75 years at 1870 AD to 1950 AD rate of growth at 0.82%: 3048×1.0082^75≈5623 people after 100 years.
This is against just using one growth rate of 0.82%, which results in just over double the starting population of 4525 people in 100 years. And remember, you won't have any incoming migration to boost your population numbers, it will be a closed system. So, in fact it looks like you were over estimating!
Obviously you can play around with the population growth rates depending on how hard a life you want to give your stranded victims.