Problem joining skeins of yarn & hole

Hi! I have two questions.
First, I completed a baby blanket but had issues with joining skins of yarn. I did the magic knot but when I pulled to make sure it was firm, it was able to be pulled apart. I may have pulled too hard but I want it to be tough since it’s for a baby, is machine washable, & I want it to last for her. I couldn’t find another knot that seemed to work so I did Magic knots to join but left long tails so that I could go back and make adjustments. Can you help? Thank you!!!

Second, while I was knitting I think I dropped a stitch. I’m a super beginner so I’m not sure if I did or if it’s ok. Can anyone tell if this is all going to unravel?!
Thank you kindly for your help!

Welcome to the forum!
The blanket is lovely and vary nicely knit. Good job.
Weave in the ends at the knot and the join will be fine. The small bit of extra yarn will work its way into the adjoining sts. I like to overlap the old and new yarn for 1 or 2 sts then weave in the tails. It makes a secure join and there’s no worry about knots untying.
Here’s a video in case it helps for weaving in ends in garter stitch. (There are others for stockinette if you need them.)

It’s hard to tell about the hole. It looks like a tiny, interesting mistake but the sts don’t look like they’ll go anywhere. You could close it up with a stitch or two with sewing thread if you think it would help.
There seems to be a yarn end near the stitch marker? That could be woven in as well. A gentle tug in all directions will usually pop out a dropped stitch which can then be “laddered up” as far as reasonable and tied off with a short strand of yarn.

I recently knitted a prayer shawl & when I went to block it, I found a dropped stitch. Dropped stitches will run until they reach a knot or yarn over. Your blanket doesn’t appear to have any yarn overs so it would be my guess it will eventually run. I fixed my drop stitch on a finished shawl by taking a length of matching yarn, using a large eye needle & looping the yarn through the dropped stitch & then securing it to the stitch right above it. After weaving in the ends, the repair was unnoticeable. Hope this helps!!!