got walked in on

Basically what the title says, but worse because I’m an idiot.
For context: I (M 20) still live at home while going to uni. my room has a lot of big windows, and I am a very lazy person, so sometimes I go into the room with our heater to masturbate instead of closing all of my curtains. The buzzing hides any quiet noises and the room has no windows. Also, when do people go into the heater room? Usually never, right? Wrong.
Big mistake, will not be doing that again. Ever.

So I was doing my thing (headphones in so I didn’t hear any steps) when the door opened and my mom stood infront of me (in the dark, with a toy, in the heater room, pants down)
Classic walk-in situation, except it wasn’t in my room, so it is absolutely mortifying and I wish I could sink into the ground and not reappear.
She barely comes down to the basement (where my room is), so how come the ONE TIME she actually comes down here is when I’m in the middle of jerking off?
The interaction that followed made it worse tbh, I said sth along the lines of “sorry, didn’t wanna close the windows” and she just replied “you don’t have to explain anything to me, I just wanted to check the heater” and sth along the lines of it being (or me acting) really weird, and then she left.

This is so awkward, and I’m gonna just avoid any interactions for the rest of the day.
Safe to say, I am not doing that again. Ever. Fucking hell this is mortifying.

Update: she looked for all the keys we have laying around (a bunch) and told me to try if one of them fits for my door, so if one good thing came from this is that I can lock my door now