Your incision seem to be well placed to me from the photographs you've included. They do however look either darker or thicker than I would like to see it three months. Ask your plastic surgeon about scar therapies with broadband light or fractional laser and drug delivery. Good luck.
Or are the implants too small and narrow
The incisions will mature and fade, but what jumps out to me as an issue that will worsen with time, is that the 300cc HP is too narrow and short. You already have more implant below your nipple than above, and have developed star gazing pseudoptosis. If you wanted that volume a mod+ would have given more upper pole, or you need a larger/wider HP device. Dimensional planning not cc's or cup sizes must be the focus of sizing. Best of luck.
Are my incisions too high?
Your incision placement is fine, the issue is that they are still very noticeable and haven't faded yet. Your scars will usually fade with time, but you may want to consider doing a series of BBL treatments to lighten the color. BBL uses filtered light energy to decrease the pigment and vascularity in the scars making them less visible. It usually takes 3 to 5 treatments about one month apart. There is no downtime with the treatment.
Incisions of breast augmentation
Your incisions will fade with time. It is only 3 months out and they re usually very red at this point. best of luck with your results.
In an effort to conceal the scar even when a bikini top might ride up above the fold beneath the breast, the scar is positioned to be a little above the fold. Your scar position looks good. It is more noticeable because it has only been a short while from the time of surgery. It will fade as time goes on and will become less visible.
Typically, well placed incisions will drift a tiny distance superiorly as the implants settle. Yours look normal - at least for here in Miami. Because smaller bikinis do not commonly fit right into the crease, a red incision exactly in the crease will show. Being a tiny bit out of the crease allows them to stay better covered.
A good scar anywhere looks good, a bad scar anywhere looks bad. You scar is still early so more visible. Hopefully it will fade with time as most do and you will be satisfied. It looks to me like your surgeon did a fine job!