Greetings everyone!

NOTE: I have some experience with foam RC airplanes but this is my first ever attempt at building quadcopters.

I recently designed and 3D printed a quadcopter frame based on the infamous F450 platform.
It's rigid enough and the arms undergo little to no deflection even at maximum throttle.

The specifications:
X Style Quadcopter
Frame weight: 205 grams
Weight without battery: 595 grams
Battery: Orange 3S 1000 mAh 40C LiPo
ESC: Generic brand 30A
Motor: A2212 1000KV BLDC
Propellers: 10*4.5
Flight controller: KK 2.1.5 running firmware version 1.19S1 pro
Tx and Rx: FlySky CT6b & FlySky R6B

p.s: I know the battery is too small for a quad but I can live with 2 minutes of flying for now! I just need to get it stabilized.

After several hours of researching the "best" PI settings for maiden flight I programmed the KK 2.1.5 as such:

1) PI Settings

Roll and Pitch
P Gain - 45
P Limit - 100
I Gain - 25
I Limit  - 20

Yaw
P Gain - 60
P limit - 20
I Gain - 30
I Limit - 10

2) Self level settings
P Gain - 60
P Limit - 60
ACC trim roll - 0
ACC trim pitch - 0

3) Stick scaling
Aileron - 30
Elevator - 30
Rudder - 50
Throttle - 80

4) Minimum throttle - 15
5) Voltage alarm - 105

Things I did before the maiden flight:
1) Weight distribution check
2) Propeller balancing
3) Electricals check
4) Mechanical checks
5) Proper ACC and ESC calibration
6) Ensured the battery is fully charged up
7) Ensured all the values are at "0" in receiver test

What happened on the maiden flight:
I had the self levelling turned off and it was strange that I needed more than 50% throttle for the drone to even achieve lift.
After I got it in the air, I didn't give much inputs but the drone was gaining altitude on its own and was drifting to the right.
Link: https://www.youtube.com/shorts/jbqxYdNi2vo

What happened on the second flight:
Turned on self levelling
I reduced the throttle scale to 80 from 90 and I guess the auto climbing was taken care of but the drone drifted to the left this time. Again, I wasn't giving any directional inputs.
Link: https://www.youtube.com/shorts/9hqbpnkzCfM

What happened on the third flight:
I guess the battery was done for and the drone was struggling to maintain altitude and immediately shot up with a slight increase in throttle!
Link: https://studio.youtube.com/video/Ylm7HNqUh5Y/edit

I request the good people here to help me out with the issue. It would be great to have the drone listen to my commands, at least till an extent!

NOTE: There doesn't seem to be any kind of oscillations on the roll and pitch axis. The only problem is that the quad just drifts awayyy!
Oh and there was just a slight intermittent breeze throughout the testing.

Thanking you,
Surya Krishnakumar