It really is too big for the space, but you can make it better. You should have some lighting and tables near. Can you move the sectional away from the window so you can put a narrow table for a lamp and other items? You could put a small table on the opposite end. Get colorful pattern drapery that appeals to you. Hang a large piece of art centered on the sofa.

Remove the ottoman
Take down the curtains - do you need shades altogether?
Light rug
Clear glass end table
And art

Yeah I need to replace all the curtains. we just moved in so its a hot mess!

You write you don't know " good color scheme"....Yes your space needs color: look through collections of draperies, fabric by the yard, art work noticing the colors: what colors go together ,which colors appeal to you and which colors are the dominant and which subordinate, or how the colors go together. You can mix and match patterns. Take the time to educate yourself and then make your own decisions.

Will your sectional fit if you rotate it 90 degrees and bring it out from the window bay?

WOW...that is tight!! That thing is way too big for that space...but if you can't return it I guess you'll have to make do. So it will just be facing a window?

Here's a living room with plants by the window, great art, white and brown pattern rug. Note sheepskin throw on the back. (Ikea sells real sheepskin.)

This brown couch has pillows, hangings, rug, etc. in textured, colorful patterns. T

The curtains are kept the color of the walls so that everything else stands out. Note round coffee table up on legs, corner lamp, textured rug.

I would go all in on your huge sofa choice and make it a super chill zen den vibe. Your ottoman is perfect bc it looks like it can snuggle into the couch and make the whole thing like a giant bed, which is so cool.

I would get curtains that match your wall color and add panels so theres plenty of fabric for them to hang correctly.

I would add a ton of pillows and blankets to up the coziness factor, and i would also hang either one huge painting or a gallery of similar paintings, like those below from PB and West Elm.

i would not go bold on the art bc the couch has become the focal point and too-bold art would make the room feel claustrophobic.

i would do lots of textured neutrals with accents of muted colors instead of bright ones.

think chunky knits, fringes, faux fur.

what is your favorite color? if youre not sure, look in your closet to see what colors you gravitate towards.

Take down the curtains and let us see what you're really working with. Can you shoot new pix and include one taken while you're standing at the far end of the sofa? How about a measured floor plan sketch? They are so helpful.