A level maths hypothesis testing help understanding topic

Hi,

I've been studying hypothesis tesing in a level maths, but i'd just like some help wrapping my head around a paticular concept.

Lets say I think a coin is biased towards heads. So i flip the coin 10 times and i get 7 heads. Staight away i know that my null hypothesis is 0.5 and my alternative hypothesis is X>0.5 - but since i got 7 out of 10 heads, i used to think "well that's 7 out of 10, so the chance of me getting heads is 0.7, so reject null hypothesis" - however when i draw out the table below using binomial distribution, I can see that the chance of me getting 7 heads is 0.12 - not 0.7 like i thought.

Where's the error in my understanding?

Any help would be appreciated

I'd also like to add that conceptionally, I know it's wrong. The probability would look like a bell curve - the chance of me getting 1 to 3 heads is really low, and then im very likely to get between 4 to 6 heads, and then im unlikely to get between 7 to 10 heads - but from gcse, I'm used to thinking that "since i got 7 heads, the probability is 0.7 (so quite high)" - like i said theres an error in my understanding here somewhere.